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measurement, tho methods of which and the men who havo achieved it are beyond the limits of a letter. Perhaps " F R. A. S." wonld upon some occasion enter Into nwre particulars, which I feel persuaded would urovo highly interesting to many readers. If we wish to find the distance between two or more places on the glebe we must measure by the arc of a great circle, and the number of degrees between the places will rive the result. The difference of longitude is an inaccurate guide except at the equator, beenu«o although every circle contains 380°, the number <>f miles lu each, as has been shown, considerably varies. The terrestrial globe, therefore, being the shape of tho earth, even supposing there were no maps upon its surface the distance between places may be ascertainedby finding their respective latitudes and longitudes and having made marks to denote them.
measure the distance between the marks and proceed
a» above, and the thing is done.
T. S. H.
THE "SHIPTONIAN" VELOCIPEDE.
8iR,_Having for a long time carefully read the different articles respecting velocipedes in your valuable journal, and being deeply interested In the subject, I found that not one of the many varieties which nave appeared were calculated, to ray mind, to economise power and ensure speed. I have therefore at hut decided upon and made a tricycle, as per photograph herewith, which I find answers every purpose admirably. As will be seen from it, the whole of the muscles of the body are brought into action, working as it does with both hand« and feet. It Is very light in construction, neat in appearance, and easy to work, and having india-rubber springs, is free from jolting. It will turn the sharpest corner with the greatest comfort, and can be steered with great nicety, There la not the slightest danger of falling, and it is safe uphill, downhill, or on level ground, as there Is an excellent brake attached, by which you can quickly ■top when descending the steepest hilt. You can also carry a carpet-bag or box on the seat behind, and on level ground or downhill a paesenger can easily be carried, and by an arrangement which 1 have already
planned (and but for sickness would have carried out), I could make it for two to work without increasing the weight of the machine more than 10 or 151b., by which means I should obtain double power, and make it to travel at a much greater sp^ed with two persons on It than with one. The levers coula, nevertheless, be put on or taken off In a few minutes, so that either one or two oould ride. The woodwork is Kreuch polished, and the iron painted black, and then varnished. Its speed is such that although I have run with several two-wheelers (and among them were some very skilful rider«), I have never seen the person who could keep up with, much less pass, me. Several gentlemen have advised me to secure it by patent, but I prefer giving my brother readers the benefit of it, if they think it of
Ebnest E. Shiiton. Vine Cottage, Knowle, near Bridgwater.
ALGEBRA.— A QUIET CHALLENGE.
Sir,—I am glad to have "C. H. W. B." agreeing with me that many of the most pretentious algebraic problems of the day are worthless. Let me remind KC. H. W. B." that even Coleneo (Alg. 8vo., p. 390) stigmatises a search after just such "impossible" roots In the Equation Papers of St. John's College, Cambridge, as "useless and profitless." Still, ■ "C. II. W. B." maintains that "algebra is extremely useful." I admit, the notation is useful; but, Euclid observed the very principle long before algebra began. In Euclid, A is an angle. II Is a triangle, С is a square, or any square, and E F, Г G is a rectangle, though only two sides of it are thus given. This Is all the good there is in i y :. Arithmetic has as much; for instance, in "Walki'ngbamo's Tutor's Assistant," by Young, interest is i, and p is principal, г is rate, / is time, a is amount ; so the formulae Is conveniently given asp r t + p - a." This is not algebra, though it may look algebraic. The real essence of " Algebra" Is in its equations; here, if anywhere, the "scie ice" is distinctive. Let, then, "C. H. W. B." adduce some common-sense question; let it be Intrinsically some serviceable affair ; let it be fairly and fully stated, and plainly worked out, Intelligible to the "meanest capacity." with answer and all; let its drift be to exemplify bow algebra is the best or the only method. And then I will engage to prove, that the algebra Ism is no advantage ; and that the point can be discovered, easier and better when the whole science of algebra has been utterly discarded.
RUAI) LOCOMOTIVE. Sir,—Enclosed 1 send a sketch of a road locomotive suitable for two or three persons. The boiler is 2ft. in dmneter, and 4ft. in height. The firebox is 20in. in diameter, and 2ft. 8in. in height, and is made of copper, sod contains two horizontal tubes. The engine consiets of two cylinders, each 4in. in diameter, and Bin. stroke, and is two speeds action. The gearing is 1 to 1 and 1 to 2, and is changed by a friction-clutch arrangement, shown in big. 2. A is the engine axle, and has two cogwheels keyed on it, one of them 7.¡In. in diameter, working a loose wheel of the same diameter on the axle B. The other is 5in. diameter, working a loose wheel loin, diameter, on the axle B.
On the latter axle is a sliding friction clutch, which engages with either the wheel С or D, aad cau be disongaged altogether, so that the engine can pump water into the boiler when standing. On one side of each loose wheel are small projections, with which the friction-clutch engages, and the gear cau be changed whilst the engine is in motion, or whilst standing, independent of any position the engine may be in. The front wheels are each fixed in a forked shaft, and connected by meane of a rock shaft to a spring-catch lever, by which the engine Is steered. The water is contained iu a small cistern under the carriage, aud the coal is placed in front of the driver. The engine works up to 1501b. pressure. This form of steam carriage may not be in accordance with the ideas of every one, yet, taking all things into consideration, 1 do not see how it can be much improved upon, and in design I have put the steam carriage through more than twenty different metamorphoses.
William Stanley, Eyre-street, Chesterfield.
PERRY'S MICROSCOPE. Sir,—Enclosed I beg to hand you sketch of my new microscopes, which will no doubt meet the approval of
same eize as drawings; the advantages they possess are as follows : —They are made to fasten to a table or block, or better, to the box which contains them, they have a reflecting mirror, a fine screw motion for focussing, a circular diaphragm for regulating theiucldent light, and last, but not least, they are strong cheap, and well-made. Fig. 1 is a front view, В Is' the square body of the microscope, R the revolving diaphragm, with four different sized boles; L the eye lens, and S the back thumb-screw for focussing; the hinge at bottom Is omitted in this figure.
Fig. 2 is a section—M is the inclined mirror resting on a block of hard woodl,- the light, after passing through the diaphragm hole. Is reflected upwards iu the direction of the eye lens (dotted / I), causing the object under examination to be well illuminated"; the light is regulated by using a larger or smaller hole of diaphragm, as the case may require. The top of the microscope has a dove-tailed groove for receiving a strip of glass x x. P is the elide carrying the lens; this slide, after passing down the groove G, terminates in a sorew, i/, which, passing through the thumb-piece S, gives tho motion for focusslug. H is the binge for fixing the box; the microscope can, however, be held between the thumb and finger, if so preferred.
The power of this little instrument may be roughly estimated at from 20,000 to 30,000. The heart and blood of a flea are distinctly seen in motion; a few human hairs resemble a bundle of faggots, and hundreds of lively beings are seen iu a small drop of water. Cheese-mites appear like horned beetles, and a flea resembles a young lobster! É. Perry.
WATER ANALYSIS, 4c. Sir,—In your impression of the 13th a correspondent signing himself " W. R." aske for my opinion as to the relative capabilities of Wanklyn's and Frankland's processes for the estimation of organlo matter in water. I am sorry he has required my opinion on the subject I must decline depreciating either, as there is no doubt they are both very good for general purposes. In their way, tho preference being generally given to the simplest, and that which is easiest of xecutlon. This process of estimation (ffanklyn's)
(Prankland's) also has eerioue defects, the greatest of which is iu the supposition that all nitrate« and nitrites are formed by oxidation of nitrogenous animal principles; BouMingault's experiments, to my fancy, prove the contrary.
With all the estimations around us of organic nitrogen, carbon, nitrates and ammonia, it is very little the public In general understand. They want,water analysed at as I}« a figure as possible, and the analyst generally reverts to "chameleon" as the most ready, and one which with ordinary manipulation gives good resulte.
As regards therelativ» proportion of organiocarbon to the nitrogen present in waters, " W. R."has Instanced :!. 1st, 2 to 1 ; und. 5 to 1 ; 3rd, 10 to 1. Now, although there seems no proportion existing between them, there really is, though in an indirect way. The third sample of water would probably be the purest, which may be proved by examining the reports of analysis; thus, above Reading the proportion Is nearly 10 to 1, andthe nitrates stand atO, but it must not always be inferred that the impurity may be measured by the proportion of organic nitrogen present, taken as regards the organic carbon, for, in one instance, a proportion of 3 to 1 was obtained, yet the weter was purer than that which contained 11 to 1. I think the best method for practical purposes is to express the amount of organic matters by the number of grains per gallon of oxygen necessary for its complete combustion.
I am not aware that it ha« been tried to convert the quantity of organic nitrogen and carbon into grains per gallon. If It bas been, andan approximate result gained only, wby it la best to use permanganate at once. One part of nitrogen might correspond to many different weights of organic residue, and the same may be said of tbe organic carbon.
Now with regard to W. R.'e " four queries :—
Franklaud's process may, I should thtnk, be applied to sewage water, but after evaporating to a small bulk the fluid should be tinlsbedata very low heat, or preferably in vacuo, to avoid loss of volatile constituents. 2nd. There is no doubt that ammonia in ammoniacal salts may be estimated by the Neesler test, but, to my fancy, normal acid is preferable. 3rd. •Same answer as.above. Question 4th. That quantity of organic matter' which requires one equivalent of oxygen for complete combustion, measured by the number of lOcbc of a chameleon solution containing 0 H9 grms. per litre, required to produce the permanent tint. George E. Davis.
STRENGTH OF CHAINS.
Sir,—I see Mr. Tolbausen, .Tun., halls from Manchester ; he may, therefore, inform me upon the follow iug :—I have read his article on "The Tenacity of Chains and Ropes." Will be be good enough to say if the formula? be gives aro practically carried out? From all f know they are not, for chains are required and do actually work with heavier loads than his rules estimate. For instance, the Lancashire and Yorkshire Railway Company at Manchester have J chains to lift 10 tons, but according to his rules It
should be over ljj Their other chains have a working load in proportion. From what I can see, the proof strains In his Table II. are more agreeable to the actual weights chains work at on cranes.
Anent his remarks In same article of the difference existing between the strength of studded and short link chains, I do not think the proportion is 7 to 0. I know from actual tests made at our works that в short link chain has broken a studded chain of equal diameter of link, and although the Board of Trade provide in their tables of proof for a scud chain to bear more than short link, they say nothing of the breaking strain or ultimate strength. You see, after a certain weight is on chains, tbe iron begins to stretch—i.e., the link beoomes longer but narrower, and having got to a certain point too stad between does not suffer it to go farther, but as strain is still applied and link extended In point of length, it separates, generally top and bottom, or at A A In Mr. Tolhausen's sketch of link. In short link or unstudded chains, however, the oval link, by being stretched, becomes straight sided having nothing to stop it, so that the strain is not applying Itself to one portion only. When these links go it is generally at the binder part, or at the neck of the shut. W. A. E. W.
give another reason. We can always tell by the form of the body whetber a man bas inucb muscle; we caunot see the muscle because of the skin, but we judge by the outward form and development, which always corresponds. The same kind of reasoning will apply to any other portion of the body, such as the stomach, bowels, lungs, &c. If any of theso are small or large, that part of the body where they are located Is either enlarged, contracted, and diminished. I consider my own head to be an overwhelming proof of the truth of phrenology. The extremes are so great, large and small, ana so various, that if a million bead* were examined I don't think one would be found Икс it, and yet it exactly corresponds with my peculiarities in every respect, including both intellectual, moral, and animal faculties. Now, taking into consideration th at the similitude is Is so exact and complete, I say most seriously that it is more than a million to one against such being the case 11 there be no truth in phrenology.
An Invkntor Ano 8xl»-taught Mechanic. [Our correspondent considers his "own bead on overwhelming prool of the truth of phrenology." We dare venture to affirm, that If he were introduced into a room of, sayhalf adosen шеи,including a poet,an engineer, a statesman, a botanist, a preacher, and a merchant, he would not bo able to distinguish one from the other by their heads; neither do we believe tho cleverest phrenologist li ving would be enabled to distinguish them if lie were permitted to manipulate their bumps in the dark. This may be an experiment worth trying.—Ed. ИМ..]
COTTON SPINNING. Sir,—Your querist, Edward Haborgham, p. 104, No. 269, asks for lnlormation about the backlog off (not baking off) motion of a mule frame, and also about the working of the cam shaft. Perhaps he will not be offended if instead of giving him the required information (which would take up too much space to give clearly), I give him a little advice which is also seasonable for other correspondents. The sum total can be written in a few words, " Think for yourself." When a person gets into the habit of asking other persons' assistance as soon as tbe least obstacle presents itself, without trying to surmount it, he has a great tendency to place no reliance at all on his own ideas, but to float along with the stream, and at length probably finds himself in the whirlpool of complete Ignorance—which, by-the-bye, is not altogether bliss—Charles Rabache to wit. For my own part I would not place entire dependence on a statement made by even such a genius as our harmonious brother the "Blacksmith," except his ideas would agree with my own, or else by careful study I could come to the conclusion I was wrong. Of course I don't mean to say that every man's reasoning powers are equal—by no meane—or that a Rabache will balance a Proctor if weighed in the scales of Science, bnt I do mean to say tbat it behoves all who intend to progress either In cotton spinning or any other study to think deeply and earnestly for themselves, and learn to depend on their own discretion and judgment. When they cannot arrive at a firm decision, or there is any doubt on the subject which they cannot themselves remove, then is the time to fall back on tbe advice of other persons. They should bear in mind that there will not always be •• Harmontons Blacksmiths," Sismas," and "Adepts," to refer to when they are "fast.' My advice to E. U. Is to go and stand behind the hcadetock of his mule, and "mark, learn, and inwardly digest " all Its different movements, and be determined to find what he requires, and I'll guarantee if he has any brains at all (no offence) he will know more in an bour than I could write in five.—I mean as regards the principle on which It works. But If my prediction does not happen to "come true." and he gets stuck in the mud, which no doubt be will before ne gets а practical knowledge of it, then I shall be most happy to help him out and render him any assistance he may require.
I hope these remarks will be received in the same spirit as that in which they are written.
The Harmonious C«tton Spinner.
quently you can make u better sample of nonr with silk than with wire. In the second place, a silk bolter, if properly constructed, does not take more than one-fifth of the power that is required to drivera wire machine that will do a fair amount of work, the third place, there is a great saving effecf using silk instead of wire, as a silk clothing if it's constructed right, and the silk put*# will last from five to eight years at an average, accu ing to the quality of »ilk; for instance, the Swiss silk wül generally out wear the French, whilst every miller will know the trouble and expense generally attending a wire machine, for if they are overfed, or a piece of fron gets in them, there is a stoppage of the machine, and a sheet of wire, or perhaps several, to put in. But with a properly constructed silk, nothing of the sort can happen. There are other advantage*, but I am afraid I am trespassing upon your space. In my next, If you think it will be of luterest generally to millers, I will peint out some disadvantages of tbe present Bilk bolters, and suggest means by which they may be obviated, as there does not seem to be the slightest doubt that ultimately, for dressing flour, siik must supersede every thing else at present iu use. E. Ьл vi tu, 92, Spring-street, Edgboaton, Birmingham.
Sir,—I was much surprised to rend the anieles on colour blindness inserted in the Mechanic. I always thought that phrenology fully accounted for such phenomena. To suppose tbat defects in the formation of the eye is the cause, is about the same as malformation in tbe construstion of the ear would be in relation to music. I know a person who is so defective in his perception of music that he cannot tell one tune from another—every tune to him is about the same; and why should it not be so iu regard to colour? Besides, some people have great difficulty in recollecting and distinguishing forms and shapes, sises and distancée of objects, localities, &c. But we never think of attributing such defects to the eye. I should like to know why an exception is mode In regard to colour. Some people don't believe in phrenology. Now, if they would take the trouble to examine it and try to understand It, I think they would. I feel as certain of its truth as I do of my own existence. If I am asked for reasons for being so confident, I will give a few. If I look at an object such as a chair or table, I know that they are such by the form and dimension of each. It is elmply observation combined With reflection. Now I do the same by the head. 1 And that the form of the head corresponds with any peculiarity which the person to whom it belongs possesses, whether intellectual, moral, or animal. I find that those who are fond of constructing, inventing, making various things haveone particular part ot the sknll prominently developed, while those who have no such Inclination have tbe same part depressed, lithe heads of all those who read the Mechanic were examined, I believe tbat the lump of coustructivencss would be f о und fully developed in most of them. I will now
Sir,—In reply to your correspondent, " Harmonious Cotton Spinner," page 204, respecting the benefit to be derived from the flyer of a roving frame leading, and vice versa, he says, that with the bobbin leading, no waste will be made, which is perfectly true, but his latter statement, that they cannot be run at as great a speed, is at variance with my experience ве far, for having had the management of three frames with the bobbin leading, and one of the other construction, we ran the three at a greater speed than the one with flyer leading, although it was going as fast as the machine would stand. Possibly, with other mokes of frames, the results might vary considerably; this I am Inclined to think is one main cause. With respect to the size for cop bottoms, 1 have used, and found the following mixture to suit best In our case—namely, 1-Jlb. best starch, and 2oz. sweet воар ; put these in a bucket, and fill three parts with water, then turn a small jet of steam Into it until it bolls; should the mixture get too sad as it bolls, add a little more hot water until you get the proper consistency. This composition was liked best by us, and 1 have no doubt will Buit elsewhere if carefully tried. Any further aid I can give, i shall be happy to do so.
Joseph B. Orossley.
Sir,—I presume from "J. S.'s" inquiry, on page 182, that he wants to know tho advantages of dressing flour through silk, over dressing it with a wire machine. As I have had great experience In the manufacture and erection of both, I will state a few of the advantages of the former method. In the first place, In a silk bolter there is, if I may so term it, no artificial means used to force the floor through tke silk, but it is done simply by the revolving of the reel; whereas in a wire machine, it is forced through by the brushes, by which means there are quantities of email greys forced through the wire with the flour ; couse
ON THE "LEAD" OF THE "SLIDE VALVE" LN STEAM ENÜINES.-ANSWER TO "STEAM SPIRIT."
Sir,—The "travel" of the slide valve, the amount of its 'lap," and the extent of it» " lead," are the three essential elements of that most important part of tbe steam engine, and these three elements, or proportions ore so Inseparably connected, so completely dependent on each other, that they cannot be considered separately or Independently ; and to speak of or attempt to discuss the effects of any one of the three upon tne distribution of tbe steam to the cylinder, without ut the same time taking the other two into consideration, is nonsense, and cannot possibly convey any practica I or useful idea on the subject.
A quarter of an inch of " lead" for a given engine, may be too mach, or it may be too little, or it may be neither, and no engineer (unless he kuows nothing of the subject) can undertake to say which it 1«, without knowing at the same time, the "travel " of the valve and the amount of Its "lap." What is the object, the use, and this history of the lead of the slide valve? In the early days of the steam engine, the slide valve was mode with but little or no lap, and when set without lead, as it frequently was, the piston would arrive at the eud of Its stroke before the exhaust port commenced opening for the escape of the steam from one end of the cylinder, and the admission of steam to the other end, preparatory to the commencement of the return stroke. Indeed, owing to the wear and slackness of the joints of the connections between the eccentric and the valve. It was ofMn late In the performance of Its duty, and In many sa old engine the Ciston often made two or three inches of its stroke efore the change took place at all ; it was then found that an Improvement In tbe Working of the engine resulted from giving the valve some lead; by-aud-bye a little lap was added by some genius, bolder and more speculative than his neighbours, and a still further improvement was found to result, inasmuch as a collateral advantage followed in the shape of expanelvo action, to a trifling extent, as the small lap and lead combined, caused the steam to be cut off a little before the termination of the stroke
From that time out, no more valves were made without lap (except In epecial cases, which I shall not notice at prêtent, os I am now discussing the common simple slide valve in general use), and new valves, with more or less lap, were put into many old engines, whoBe valve cheBts were long enough to accommodate longer valves with longer strokes, but, In general, the valve chests were not long enough to admit ot the improvement, and hundreds of these antiquated machines have struggled on to the preeent day without improvement, and not susceptible of any, and, In all human probability, will see most of us laid under r be " sod," who now smile at their antiquated proportions, their grotesque appearance, and their Insatiable appetite for fuel and water.
ft will be seen from the above, that the lead was a very Important thing with valves which hod little or no lap, and short travel, an* tbe proper amount of It was the subject of many a warm dispute amongst the old millwrights (the engineers of former days), and I have myself been sometimes specially privileged, when only a very young apprentice, by being permitted to be preeent at some of their Saturday night aad Saint Monday discussions, and of course I thought the disputants were wonderfully clever fellows, and my great ambition was, in future years, to become such a "shining light" as "big Martin Murphy," or "Red Jack Carter," or "Old Dick Mend," or "Boh Thomas" (all these luminaries have disappeared below the horizon years ago, and have gone to that place where the "wicked cease from troubling, and the weary are at rest" R.I.P.), but In after years. I changed my mind, as the conviction forced itself upon me, that all which these "eminent authorities advanced, could not be "gospel," Inasmuch as во two amongst them could agree on that (or any other) subject, notwithstanding the amount of whiskey they drank, and the quantity of chalk they osed In drawing diagrams upon tbe tables, and walls, and floors of the publichouscs, and the incredible amount of profound balderdash they talked In explanation of them, and finally, the quantity ol " skin and hair " they made fly from each other when weaker arguments failed or were exhausted, the whiskey all drank, the money all spent, and the chalk all used up.
With «Ives of modern moke, and whose lap ii considerable, вау one-fonrth or one-filth of their travel, the amount of the lead is not so important, and the difference between an eighth inch, and a quarter Inch, and three eighths inch of lead in their effects upon the distribution of tbe steam, is very inconsiderable Indeed. "Steam Spirit (query 2532, No. 26S) asks me "why I would give во much lead (Jin.) to the engine in question ¿Reiwot's " engine; see my letter on page 39, No. 202). He says, •• he should have thought a quarter Inch of lead decidedly too much for any stationary engine, except it was a very high piston speed." "Steam Spirit" has not favoured Ub with his reaiona for thinking Bo, "he has given no account ol the faith that is la him."
Now let us Investigate the subject properly and systematically, throwing mere opinion, and hearsay, aud the rule of thumb, and tradltlou, aside, and endeavour to come at the actual facts of the case, and I will venture to say that we will all find ourselves both 4* wiser and better men " on this particular subject, at the end of the discussion, than we are at the beginning. If we do not, it will be no fault of mine, for I shall "put down " all I know about It. The lead of the valve exercises an Influence on each of the four principal events which tako place in the distribution ot the steam during the stroke of the piston, viz., first, "pre-admission," or the admission of steam to the cylinder before the termination of the stroke. Second, "admission proper" which ends in the "cut off." Third, "expansion, which ends in the " exhaust," and fourth, "compression."
For the purposes of this discussion, I think it better first to take the case of a common slide valve, worked by a single eccentric, in preference to such valves as I recommended lor "Kelwots" engine, as they are compound valves to a compound engine, aud the investigation of their action beyond what 1 said in my former letter on the subject, would be very tedious, and would require many illustrative diagrams, and so must stand over till we have gone fully into the performance of the "simple slide valve."
Take a valve of the following proportions, via., 61n. travel, lln. of lap. on the admission edges, and having neither lap or deficiency on the exhaust edges, and worked by a common eccentric. The distribution of the steam by this valve, under three different leads— viz., one-eighth, one-quarter, and three-eighths of an inch, is shown graphically on the annexed diagram (Fig. 1), which n»» reference to a horizontal engine or, in fact, to any direct-acting engine equally. The semi-circle Is the path of the crank pin, and the diameter A B represents the stroke of the piston, in this case 20in. The distribution of the steam under the fin. lead is shown by the short dotted liues t" C" £'", which are the positions of the crank. The distribution under the jm lead is shown by the full dark lines, P" C" E', and I" C E' show the distribution wlieu the lead is tin.
This diagram shows faithfully, at a glance, the very trifling effects produced by the alterations of the lead of this valve within limits which X presume are seldom exceeded in practice, for few engineers would think of giving it more than j|in., or less than |ln. of lead. And first aa to the effects on the pre-admission*. Under the }ln. lead, the valve begins to open when the crank is at P" (going in the direction of the arrow), or within 91 degrees of the "dead centre line." Under the Jin. lead, the crank is at P*. or 7° from the centre, and under the Jin. lead, the crank is at F, or 31° from th* centre, when the valve begins to open for the admission of steam. The crank in each ca*e has approached the centre line so nearly, that the ** veraine " hay vanished, and the piston has virtually ceased to move, and consequently the alteration of the lead can have no sensible effect whatever on it.
The "out off" comes next, when the crank isatC C*. C", and it fs apparent that the alteration of the iead is more felt on this event, as measured on the motion of the piston, although less on the angular motion of the crank than on either the "pre-admissions M or the exhaust at E' E". Under the |ln. lead the steam is cut off when the crank is at C", and the piston has made I5iln. of the stroke. Under the iinlead it i# cut ofl when the crank Is at C", or NSIn. of the stroke, and with the |in. lead It is cut off at C, or lfijiu. nearly, the whole difference being comprised within leas than lin, or leas than one-twentieth of the stroke, a trifle not worth speaking about. Lastly we come to the exhaust at E' E* E*Cand we see that with Jin. lead the exhaust takes place when the erank is at E", origin, of the stroke; with theiln. lead it takes place when the crank is at E*, or 18#fn., and
"distribution" by a further reduction of the game valve's travel to 3ln., and Fig. 3 illustrates fts performance under this condition. A single glance at the diagram shows that the influence of the lead Is vastly increased, and that its power of altoriug the time of the occurrence of the several events La very great, as is plainly shown by the wide-spread positions of the lines representing the crank at the times of their occurence.
"Pre-admission," in Fit'. 3, occurs under the Jin. lead, when the crank is at P", and is vet 2,'>" from the horizontal line, and the piston is a full inch from the termination of its stroke. Under the Jin. lead the crank is at P* 15.J° from the horizontal, aud the piston I* full ]in. from the end of Its stroke, and under the Jin lesd the orank is at I" 7°, the versine has vanished, and the piston has ceased to move when pre-admission occurs.
The "cnt or?" occurs under the Jin. lead, when the crauk Is at C", and the piston ha* made ojin. of its stroke. Under the Jin. lend, the crauk is at C", and the piston has made sjin. of its stroke; and with the Jin. lead, cut off occurs when the crank is at (/, and the piston hns made lojln. The exhaust occurs with the Jin. lead when the crank is nt E", and the piston tins made Hln. of its stroke. With the Jin. lend the crank is at E', and the piston at l.'tjln.; and with the ,Sin. lead tho crank is ot E', and the piston at lojtn. of us stroke when that event occurs.
And now to recapitulate :—
Referring back to Fig. 1, with a valve of 6in. travel and lln. of lap, we see that within the limits of lead investigated—viz.,|Jin. and Jin., thore Is really nothing to choose—one extreme is just as good or as bad as the other, and tho medium is no better and no worse than either, and whether such a valve Is set with Jin., Jin., or Jin. of lead, can make no appreciable difference in the working of the engine, let it be high or low piston speed, and the proportions indicated here (of travel five times the lap), Is one In very general use, and is a very good proportion too. But the case assumes a slightly different aspect in Fig. 2; with the travel of the valve reduced to lin., the influence of the lead is more felt on the times of the occurrence of the several events of the distribution than in Fig. 1; but who shall say, even in this case, which of the leads is best, the Jin., the Jin., or the Jin., for the difference caused by them in the distribution of the steam Is not much after all. On the "pre-admissions" it is not worth notice, and shall receive none. On tbe cnt off, there is a difference of only about ljln and on tbo exhaust, the difference is but lin. If the lin. lead cuts off tho steam a little sooner than the Jin. or the Jin., It also exhausts it earlier than either of them, and the three expansion periods are nearly equal. The Jin. lead uses a little lees steam, but It also does a little less work than either of the others, and either of the three exhausts the steam quite early enough for the very quickest piston speed in use. Clearly, then, we have as yet seen no great reason for preferring ono degree of lead over another, within the limits investigated. •
We have now only to consider the Influence of the ditterent degrees of lead under the 3ln. travel, Fig. 3. In this case, the very early pre-admission caused by the Jin. lead, which occurs when the crank is at P"', some would perhaps consider objectionable, because the piston has to move during the last Inch or so of its stroke against the incoming steam, but when that is said, I believe all is said which can be said against the Jin. lead, and, after all, this early preadmission is not a positive evil, because there is no power lost by tho piston having to move against the steam tbe last inch of the stroke, inasmuch as the power It exerts In
doing so, is stored np in the valve chest, rcodyifor u»o on the return stroke, just like any ordinary spiral Bprlng, which will restore to the o'oject compressing or winding it up, all the power employed In that operation, lbe Jin. lend causes pre-admission at P", when the crank is within 15J° of tho centre line, and tbe piston has scarcely Jlu farther to go; and If, ft* I nave just shown, there is no substantial objection to the Jin. lead, on the gmuud of early pre-admission, there can, of course, be none against the Jin. lead, and as to the Jin. lead, which causes pre-admission at P. and when the crank la within 7° of the centra line, and when the piston haa ceased moving, I need say nothing about it.
Then as to the cut off. The Jin. lead causes this to occur when the crank is at C'", and the piston has mode tl}in. of Its stroke. The Jlo. lead causes cut off wben tho crank is at C and the piston has made 8Jin. of its stroke; aud the Jin. lead cuts oft when tlie crank is at I' . aud tbe piston has made lOJin of Its stroke.
Kxhaast occurs with tbe Jin. lead, when the crank Is at K". and the piston has made 14ln. of its stroke; with the Jin. lead it ocenrs when the crank t» at E", and the piston is at lSJln., and with the Jin lead, the crauk is at K', and the piston Is at 16}iu. when exhaust occurs. Now, the OJIn. of steam admitted under the Jin. load expands into 14ln. previous to exhaustion, or-Vr times its original bulk, aud If its efficiency during admission be represented by 1, Its total efficiency will be equal to 17 nearly. The 8Jln. admitted under tbe Jin. leaxl expands into 15Jin., or 1142 times its original bulk, and its efficiency during admission, betug 1. its tut.il efficiency is 1-6 nearly.
The lojln. admitted under the Jin. lead, expands into liWin., or 1-itt times Its original bulk, ana its total efficiency Is represented by 148, nearly; this shows an advantage in favour of the greater lead, as it develops more of the expansile principle of the steam than luu lesser leads. I have only noticed the expansive action which takes place before exhaust, as alter that event ocenrs, the reduction of pressure with large porta is so rapid and complete as to leave no pressure on the piston worth notice; but whatever It is, it is still In favour of the Jtn. lead, as it acts for a greater length of the atroke In its case than it does with eiUier ol tbe lesser leads.
I have now said all I can think of at present on the subject of the "lead of the elide valve." I have Investigated the effects of three different degrees of lead on the three principal events of tbe "distribution," with three different amounts of travel, or twenty-seven aspects of the question altogether, and these include all that is done in general practice, as far as the common single slide valve is concerned, and I must confess that 1 nave not been able to see or to show any good reason for preferring one degree of lead to another, within the limits I have discussed, except in the case of Fig. 3, there is a little advantage in using the Jin. lead, as it gives more expauslve action, and consequently a greater economy of fuel than the others; and tbe same may be said in a much less degree of Fig. t, and a still less degree of Fig. 1.' I now leave the question here, and hope to see it taken up by abler hands, for I agree with "Steam Spirit," when he says that he "would like to see this question well argued ont In these columns by some one who can fight." "Steam Spirit" asks me for a "single rule " to And the proper weight and size of engine fly wheels," I am not surprise! at him asking , such a question, as the rules generally given in " the books,' are so elaborate, and so deeply learned, aud withal so contradictory, as to knock a plain practical man into a complete "doldrum," if he only looks at them, and to drive him back upon the good old '* rule of thumb" for his guidance, and I am by no means sure but that the rule of thumb, In the bands of a man of good sound judgment in mechanical matters, is infinitely better in this case than any mere "book rule" I have yet seen, but I cannot give "Steam Spirit " my mind upon this subject, till my next letvr.
James Babxervillc, Manager, City Foundry,
STEAM PROPELLERS IN STEAM VESSELS. Snt,—Your readers may be Interested to learn that ere long It is probable that steel will be extensively employed as a material for propellers in steam vessels, which are not uufrequently disabled from their fracture or that of the screw shaft, several such accidents having befallen Cunard ships of late, vide Samaria and Siberia. The ex periment has already been tried with entire sucoess, and several large owners of steam lines are discussing the question of their adoptiou. The advantages are, one-third diminution in weight, a vast increase in strength, and a certain elasticity quite absent in cast-iron, it is probable also that with the fine edge which can be given to the blades, the embarrassing'aud costly delays which at times occur through fouling of hawsers would be prevented, as they would be at once out by the revolving screw as soon as any strain was exerted thereon.
SYSTEMS OF SHORTHAND. Sir,—I am very much pleased with the present form of your or "our1' Mechanic, and look forward to Its nrrival every week as a choice bit of mental food. I should think that amongst your correspondents you number a small army of shorthand writers. I should much like to see a few opinions on the comparative merits of different systems of shorthand; the ease or otherwise with which it may be learned; tho probable time required; and tbe advantages and disadvantages (If it Is possible that there con be any) of the knowledge of this art. Any information will be thankfully received. Hehmit.
EMIGRATION.—TO " COTTON CLERK." Sir,—I will at tbe earliest possible moment'attend to your request, both as regards Canada and Australia. Can you not during tho interval acquire some knowledge of farming? You will find that the information required to ensure prosperity is not intuitive, bat must be learnt.
THE SOLAR SPECTRUM.
Sir,—I gather from a perusal of your Interesting paperofthe 20th inet., that some of your read«TM are in doubt ан to the dark lines of the solar spectrum being really due to absorption in the solar atmosphere.
Permit me to remark that a final proof of this lies In tbo fact that when n vividly Incautlescentprominence is seen on this dun by the method I proposed in 18641, some of the dark lines change from dark to bright.
Mr. Proctor, who writes (page 211) that' an increase in the density of our own atmosphere would not increase the breadth of the atmospheric lines (that Ы the dark line produced by the absorption of our own atmosphere) has doubtless overlooked the results of the experiments carried on by Dr. Frankland and myself, in which wo show that increase of density *toes increase the breadth both of bright and dark spectral lines.
/. N обман Lockyir, 4, Victoria-road, Finchley-rd., London, N. W.
THE SOPER RIFLE.—MATHEMATICS.
Sir,—In the account of the .Sopor гШе, I should have stated that it is fixed by means of two screws, not one, ae mentioned.
"T. J. O'C." wishes for some information upon algebra; If he will kindly have patience the reward will follow. We mathematicians can scarcely claim more of your space than we do now. This Iu.lv be seen by the fact that your waste paper basket eontains no small quantity of paper i-poiled by being covered with " letters " and figures, flow do I know this? Why some of my longest lucubrations have been found therein, helped downwards by a shorter if not better solution, it is really a difficult matter to cater for so many and diverse minds, nnd I for one give you great credit for the discrimination used, and the excellent results obtained.
Would " Bernardin," and R. A. Proctor, Esq., kindly favour me with their private addresses through our Editor?
С. П. W. В.
[We certainly do not Usert all the mathematical matter sent us, and for the followiug reasons. It would occupy too much space, and it is difficult and expensive matter for the compositors to compose from manuscript copy. When the slightest mistake occurs in the formula; very frequently nil the calculations are thereby vitiated. We have, however, too much respect for " С H. W. В." to give the waste basket many of his contributions, and particularly what he eontributes on other matters under another name— Ed. E.H.]
VELOCIPEDES-THE "PHANTOM" WHEEL.
Sir,—It may be mere stupidity on my part, or It may be that I am not yet used to the "style " of Mr. Henry W. Reveley's English, but for the life of me I cannot make out the drift of his letter on page 131.
If I rightly understand what he says about the "Phantom " wheel, I must tell Mr. Keveley, with the greatest deference, that he altogether misunderstands us. We bave never " proposed 'ythin plates for rubber tires. We actually make and use half-round rubber tires ¡x |, which we are prepared to match for speed, safety, ease of work, and lasting qualities, with anything he can bring against them in the way of velocipede wheels. He tells us that the tires of what I suppose I may call the velocipede of the future " must not ' be tired in the way we propone. Well, in spite of this dictum, we are satisfied with what we ure doing and have done with our rubber-tired wheels for several months past.
A word, too, aa to the "velocipede of the future." "Would it not be a real mercy to the general reader, and a grateful boon to practical velocipedista as well to confine mere proposal! and scheme» such as this of a "light carriage for 30 miles an hour with a ilow treadle movement," and all the tall talk about them to occasional special numbers? We shall never be tired of your admirable articles and illustrations of machines which have been actually made and driven, «ven where they have only дот a very short distance. But let us have done with railways to the moon.
I remember being very much struck at hearing Mr. <ïU)Hher, the eminent aeronaut and astronomer, express at a meeting of scientific men an ironical desire that the Society should be favoured with a series of papers "On Failures," for he felt, he said, that a great deal more good could be accomplished if gentlemen would be I rank enough to come forward aud confess wherein and bow their experiments had been resultleas than by the continued iteration of new theories and speculations as to what might be done. Now may it not be so in regard to velocipedes? How many of your readers may nave etopped short on the threshold of great Improvements, which may be reached after all with a little help from the experience of some one else 1 Try and induce aome of your correspodenu to go in for this part of the subject. It will be a healthy change, and may help to keepothers upon «olid ground. If Mr. Keveley could only be induced 10 put together his 30 miles an hour light carriage with slow walking motion, and all the rest of it, what a nice chapter he might be able to write for your new heading!
J. A. Mats, Manager and Secretary, The " Phantom"
Veloce and Carriage Wheel Company (Limited), 10
King-street, Tower-hill, London, КС.
COLOURS OF STARS, Ac. Sir,—Will some of our astronomical readers Inform me which is the proper time to see the correct colours of the atara? Our " F.R.A.S.," Mr. Proctor, and Mr. Webb call Sirius a pure white star. Now I do not think I am colour-blind, but, to me. It appears at night which I should call the proper time to see the stars), a pure green with dashes of red ; several friends agree with mo; and in Lockyer'» " Elementary Lessons " It is classed as a green star. In twilight It appears white, but not soas the night advances. Will Mr. Proctor or" F.R.AS." kindly give me the comparative bright
ness of the chief nebulas visible toa 31n. achromatic, so oa to get an idea of what I am to expect, when looking for the fainter ones. err
"Omicron" stated that the light of D'Arrest's comet was to be 0-126. What does that mean? I beg to second the resolution proposed by .1. Brown, p. 228, in regard to an Index for "Notes nnd Queries"; as it Is much wanted and ought, I think, to have been done before. I hope it will be carried unanimous! v.
MESSRS. CUNNINGHAM AND MCCARTHY'S IMPROVEMENTS IN MOTIVE POWER.
Sir,—The Invention described in your last number (page 233) in a most extraordinary one, especially as put forth by gentlemen evidently possessed of great knowledge in the practical details of machinery. The application of spiral springs as a motive is a very old device, which cannot be usefully employed except In the case of watch and clock machinery, or such like, and for this reaeon, that the power required to wind up such spiral springs is greater than that required to do the actual work proposed to be accomplished, owing to imperfect elasticity, friction, and other obstacles.
But Mesare. Cunningham and M'Carthy are not content with these so-called Improvements in motive power, their aim Is apparently perpetual motion. For by having two separate spiral springs, they propose lhat;whlle one is uncoiling and driving the carriage, it shall at the same time cause the other to be wound up by means of Its windiog wheel touching the road, so as to be ready to act when the first shall be exhausted.
Nothing more or less than perpetual motion.
Henry W. Keveley, Reading.
"HOW TO KEEP THE CLOCK RIGHT,"4c.
Sir,—I am sorry to see that " Luke the Labourer ', (p. 62) gives such an unfavourable notice of the book. '* How to Keep the Clock Right," especially as it contalus testimonials from such astronomers as Sir J. F. W. Herscheland the Rev. J. Challis, M.A.. F.R.S. The former distinguished astronomer says that "so far as he can perceive, the method seems to be a very good way of keeping exact time, and very little costly, as well as attended with hardly more trouble than would be required for merely uncasing the telescope and looking through it." The Kev. J. Challis says, " he considers the method to be good in principle, and to be very practicable." I have not yet tried the method, but intend to do so; and I confidently expect to get the time within а ¿sec. by observations of three or four stars. I think " Luke the Labourer" may overcome his difficulty if he constructs a chart of the 350 stars in the zone t s be observed, carefully denoting the star magnitudes by block discs of variable diameters: 8th magnitude stars should be represented by dots only just visible. The catalogue numbers should be placed near each dot. I have made a chart of this kind—scale 'Sin. = Io. I can readily distinguish the mapped stars from others when directing a telescope to the zone on a clear night, on a cloudy night I would recommend "Luke" to observe several supposed catalogue stars, and then to argue from his observations to the catalogue by comparing the time intervals, rather than argue from the clock to a star. I humbly endorse the opinions of the great astronomers above mentioned with regard to this method of keeping the clock right
Will " F.R.AS." or Mr. Proctor kindly answer the following questions?
1st. Wnat is considered to be the best method of determining longitude by astronomical observations?
2nd. Are all or most of the visible occultations of stars, of which data are given in the '• Nautical Almanac," observed at Greenwich or other public observatories?
3rd, Cau I obtain the observed times of disappearance and reappearance of certain stars as seen at an observatory whose longitude is known; so that by comparing these times with the observed times at any station the error of the lunar tables ;might be eliminated and the difference of longitude found by the method given in Loomis's " Astronomy?"
I should like to know the result of any observation of the moon on the meridian made at an observatory for the purpose of detecting errors of the lunar tables; also what is the most probable value of the earth's
Kolar semi-diameter, tue equatorial semi-diameter Bing considered as unity? I have only lately noticed that Bome corrections are required In the foriuubr for computing eclipses and occultations, and for determining longitude from observed eclipses and occultations, given in the Appendices to the "Nautical Almanacs" for 1836 and 1837. These formula; were prepared when В иск hank's Tables of the Moon were used; but since they »re now replaced by Hansen's Tables the constant
i log. of — = 9-435.17 requires correction. P I find that for the present ephemcris of tbe moon, j log. — = 9 43608; and this constant must be used
P Instead of the former In the formula;. This log. appears on pp. 130,134, 175. Ш, and is used In determining two constants on p. 177: here the oge 05639* and 2'W234l must bo used Instead of the legs. 0 5646» and 2 99167 On p. 134 the nat. number -2725 must be replaced by '2729. Of course these alterations are well known to practised computers; they may not, however, have been noticed by some fellow amateurs.
RA. AND DECLINATION OF STARS, Ac.
Sir,—" Scorpio " asks for s book rontainingtbe above. May I be allowed to recommend Mr. Proctor's " Handbook of the Stars," containing the correct places of 1500 stars from 1 to 6 magnitude, end also л very easy way for laying down the meridians, 8tc. It is a 5a. book, but very useful. I wish to tbank " Amateur," page 236, for description of psneratic tube. Although I did not do it right at first. I succeeded with a small tourist glass, and was greatly surprised nt the continual increase of power. Could " Amateur" gire the reason °
H. W. Bishop.
THE ELLIPTICTTY OF ТЕК EARTH.
Sin,—That Mr. Beardsley should nave failed in the difficult task proposed to himself has probably surprised no one who has devoted himself to the study of astronomy; and however satisfied he may be with his own reasoning, I may venture to say that he has convinced none of your numerous readers; and further, I think I can also say that tbe reasoning of your corre, spondents will have failed to convince him.
The answering arguments that Mr. Beardsley'e letters have drawn forth, while they have been, perhaps,, as good as his reasoning ha» deserved, have beex weak. I believe one gentleman asserted that the fact of a person's travelling continuously in a certain direction, and arriving at the point from which he started, was a proof of the sphericity ot the world; another, that if the earth were flat, it would be possible to lall over the edge. It is tbe use of such weak arguments as these, nnd which are easily confuted, that give rise to the doubts in the minds of aome of the truth of the generally asserted figure of tbe earth. Neither am I satisfied with the course Mr. Beardsley has pursued. I hod hoped that we should bave seen in his letters something new, and not have been treated to a repetition of the childish arguments that we are so familiar with. In fact, I had trusted to have seen something original in his letters, but have been disappointed. Perhaps the fault was mine; for I had without sufficient reason concluded that as Mr. Beardsley was not a follower of Newton and Laplace, he was necessarily the Inventor of a system himself. It seems to me now that Mr. Beardsley is In the fortunate position of being able to throw stones at other people's glass bouses, without erecting one of his own for other people to throw at.
But supposing that Mr. Beardsley limited himself to the wide field of overthrowing the existing théorie«, there Is still much left for him to do; for he haa yet to consider those /acts with which astronomers more particularly concern themselves, from which the figure of the earth can be deduced without measurement of its surface, and with which geodetical instrumenta have nothing to do.
I bad hoped to have seen the disciple of the school of "Parallax" treat of tbe theory of precession and nutation, and to have seen him overthrow tbe reasoning of astronomers that deduce from tbe magnitude of these quantises, taken In conjunction with the density of the earth, the amount of its elllpticlty. Nor did I think that the observed inequalities of the moon'e motion would have been forgotten and left unexplained; and I am led to think that It is just possible that Mr. beardsley was unaware that astronomers are able to discover the form of tho earth by other means than measurement of arcs of meridian and pendulum experiments.
It may be interesting to some of your readers to see collected the figures that express the elllpticlty of the earth deduced from different methods. The general agreement between them Is euch as to confirm, were confirmation needed, the expressed opinion of philo* sophers that the form of the earth does not differ greatly from an ellipsoid of revolution. Airy's discussion of what he considered the most accurately measured arcs of meridian gave с = 0 003352.
Beseel, from eleven arcs of meridian, some tbe same and some different from those selected by Mr. Airy, and discussed by a totally different method, deduced e = 0-003356.
The elllpticlty deduced by the Astronomer Royal from the consideration of the pendulum experimenta equals 0 003471.
The phenomena of precession and nutation give for a result e = 0 01)3323; and finally, the discussion ef the inequalities of tbe moon's motlou, in longitude and latitude, give respectively e it 0 003387and e = O00337O.
A Blight discrepancy is noticeable In these figures, but во slight that our surprise is elicited, and our admiration excited, that modem measures and mathematical analyses have been carried to such a point of perfection as to make even these small discrepancies a matter of controversy and speculation.
Should Mr. Beardsley be prepared to battle with the more intricate problems of astronomy, the resulta of which I have mentioned here, I wlli venture to beg space for him, although, I must confess, it is only for the gratification of my curiosity. O.
CARBON MONOXIDE-STANDARD SOLUTIONS.
Sir,—Your querist, "P. P. W.." can obtain caibonous oxide by many other means than those he mates —lor instance, by direct combination of its element«, or by substitution, from cyanide of potassium, or terrocyanofrcR, or cyanogen itself. By decomposition ot more complex bodies it is also obtained, an by the oxydisation of ethyl, acetvie, methyl, Ac.; or the dec о m po Rit i ou of furmfc acid, oxalic acid, &c. None of these methods depend on carbonic acid for tbe formation of oxide of carbon.
"Aqua" can prepare standard solutions on many bases, as Mohr's, Griffin's, Sutton's, British Pharmacopoeia, Ac. The best mode Is to use as a standard normal solution one of a single equivalent In grammes dissolved In one litre of pure water, and for a decinormal standard a tenth of an equivalent per litre. Then, of course, every cubic centimetre used indicate« an equivalent in milligrammes of the substance being estimated. As, for instance, to take a very simple ease of estimating nitrate of silver, a normal solution will contain ô8 5 grammes per litre of sodic chloride. Suppose we find it requires 20 cubic centimetres of this solution to precipitate the silver as chloride from the nitrate this then indicates 20 equivalente In milligrammes of nitrate of silver, or 20 timed 170 milligrammes of the river salt—that is to say, A 4 grammes. If "Aqua" wishes for practical details, he cau have them; and reference to your number for May 27th, letter, *' Water Analyses!" will show him an answer to his query about permanganate of potasa,
"A Sister Reader" will Und it quite impracticable to dissolve plumbago.
THE ЕГЕ.-INVERTED PICTURES.
Sir,—It is an established fact,and well known, tha , all objecte presented before our eyes project an invert ^
picturv upon tbc retina, bat the picture, when transmitted -to our mind, seems to us upright. The question hue therefore been often repeated, does our mind, in reality, receive an Inverted or an upright Image? Without investigating any of the explanations with which we meet In books on optics, allow me to give oue fact, which may throw я new light upon this question :— I once knew an Intelligent little boy, then about, or nearly, five years of age. His eyes seemed to be in perfect order, yet at candlelight, in certain position!", when an observer was in the line of the reflected ray the left eye was crystalline; there was no black colouring matter in the interior, no optic nervi*—in fact, observations proved the boy to be blind lu the left eye. Although blind on one side, the boy amused himself by drawing simple objects, such as horses, dogs, fowls, and honses, very correctly, upon paper and slate, but ait these drawings were inverted lupfide down) The boy was often told that his drawings were upeido down, but be smiled and said "They are perfectly right." No doubt he saw all objects in that position. The bright little fellow soon proved that Ilia lett eye was an exception, was a fearful malady; it inflamed, and fungus developed itself out of the cavity. After about tea months' suffering the boy passed away. While he woe ill, in hours free from pain, he still followed his amusement, drawing inverted animals upon slate, which again proved that with one eye, and one optic nerve Inverted, impressions were transmitted to his mind.
i may hero observe that the above case is different from any case where an eye may bo lost by accident. In the latter case the optic nerve is seldom—it-, rudiments, however, are never—destroyed. With the boy tho very rudiments of the optic nerve on the left side were wanting ; In its place were the rudiments of the fungus. Taking all the circumstances in consideration, 1 can only come to one conclusion—that with a pair of normal eyes the image presents itself to our и i i ml in an upright position. The eingle eye presented iuverted images; double combinations produce upright pictures. It seems in normal eyes to be this :— The inverted pictures on the retina are travelling along the optic nerves; the latter, as we know, interlace each other. Here an interchange of impressions must take place. In this very act the pictures are reversed, and, resolved into oue upright picture, presented to our mind.
Tue Welsh Shepherd.
THE MOTIONS OF THE MOON AND EARTH.
Sir,—For year« past there has been a great deal of quibbling about the proper term to use to express the motion of the moon in relation to the earth. This motion luot taking into consideration external disturbances) is precisely what it would be if tho moon formed part of an immense globe, having the eurth for a centre and reaching beyond the orbit of the moon, the period of rotation on Its axis being equivalent to a lunar month. Allowing for the accelerated rotation of the earth, it would seem that the earth and tbe moon might be portions of the same solid globe, and yet retain the same relative motionsand distances that they have at present, and that the moon revolves round the earth under precisely the same conditions as any portion of tbe circumference of a globe revolves round the centre of the same.
SCIENCE FOR THE YOUNG.
Sir,—Will you allow me to draw the Rev. E. Kernan's attention to a few errors which he has committed in his treatise on "Science ior the Young." Under the head of law third, be «ays, "Time is required to overcome the inertia of a body whether at rest or in motion. When force is applied to a body, я certain amount of time is necessary for the production of the effect of motion or resu" In this statement he has committed я serious error by confounding tbe term inertia with я body in motion as well as at reet. Inertia has nothing whatever to with a body in motion any more than momentum has to do with a body at rest. Let us ask ourselves, what is Inertia? and what is momentum? The answers to these questions are extremely easy. The quality which enables я body to resist the sudden communication of motion is termed its inertia, aud the quality which enables a body to resist tho sudden extinction ut motion is termed its momentum. Therefore, ho should have written law third, a« he calls it, time :—" Time is required to overcome the inertia of a body at rest, or the momentum of a body in motioB. When force is applied to a body, a certain interval of time is necessary to produce the effect of motion or rest in tho' body. Where doei he Intend to insert tho law of reaction, which is an axiom of statics, thut is, a selfevident truth, or one which admits of no other proof than universal experience, aud which tells us that action and reaction are equal and contrary, that is to •ay A cannot act mechanically upon к without A ttself being reacted upon equally, but in an opposite direction, or, in other words, that whatever force оно ri»id body exerts upon another rigid body, the latter oppose» that toree by an equal force, which is called iti reaction. Thie law is of as much importance as any other in statics.
Again, fit p. Г'Л he arranges the divisions of mechanical philosophy in tho fouovtlng manner — via., statics of solids or statics, statics of liquids, hydrostatics, statics of gases, pneumatics, dynamics of ■olids or dynamics, dynamics of liquids, hydrodynamics, dynamics of gases, pneumatics, palmatics (acoustics) of solids, liquids, gases. Now, I must tell Mr. Kernan that he could not have written them In a more inexplicable manner, and he has not alone written them in this inept manner but tie has placed the «talles oí gases and the dynamics of gases under the same sl«nidcatlon—namely, pneumatics, which is most absurd, and not to bo met with in any standard work on the subject. The above division« of mechanical philosophy when properly written should bo arranged a« lollows—vi/.,
1. Statics—the rest or equilibrium of «olid bodies under the influence of forces.
2. Hydrostatic«—the rest or equilibrium of fluid bodies under the influence of forces.
3. Aerostatics.— tho rest or equilibrium of aeriform bodies under the influence of forces.
When motion is the result of the application of forces to these conditions of matter, we have the following subjects :—
1. Dynamics—the motion of solid bodies produced by the influence of forces.
2. Hydrodynamics—the motion of fluid bodice produced by the influence of forces.
2. Aerodynamics, or Pneumatics — The motion of aeriform bodies produced by the influence of forces.
I think the above arrangement is much superior, both as regards simplicity and comprehensiveness, than that given by the Rev. E. Kernan, becanse each signification is clearly defined, whereon in hts arrangement none of the terms statics, dynamics. &c, are explained at all. I see he has added a new division relative to the vibration of bodies, and which he consider« might be entitled palmatics. Well, I will not dispute with him as to this division, as it mnkes very little matter whether it be considered as a separate division or not.
Thomas J. O'connor.
THE MIDLAND AND WESTERN DISTRICTS OF IRELAND
Sir,—Will you kindly nllow me the space In the English Mechanic, to ask a question or two, which I shall leel obliged if some of our courteous geological friends will answer. Travelling through the Midland and Western districts of Ireland, I passed over immense deposits of limestone, some specimen« of which were literally crowded with fossil remains, which I believe are called Eucrinites, I wish to know whether they are uuinial or vegetable relics, and whether they existed in the sea or in fresh water. They occur in great abuudance near Athlone, in Couneinaro, and Joyce's country. Tbe deposit assumes a différent appearance, that ot a mottled grey marble, well suited for building purposes. Other rocks in the vicinity of Ballanahineh gave unmlstakeable cvideuce of I think a good per contage of copper, perhaps not sufficient to pay for the working. I should like the opinion of one who has visited the same locality, and better versed in mineralogy than myself. I was much surprised to hear that this beautiful part was but seldom visited by tourists, я fact I can only account for that its beauties are so lutle known. To tue angler it offers rare attractions; the Loughs Ina and Glendalough are well stocked with salmon and trout, aud are situated wtthin au easy distance of the halfway house (usually called Lynch's Hotel), and the Recess Hotel, both of which are passed by the mail cars ел raufe from Galway to Clllden. To the nntlquurian special interest would be attached to the old abbeys of tbe neighbourhood, the old abbey of Cong being the resting place of the Inst Irish King. Part of the cloisters have been restored, and the whole ruins are kept In repair by Sir Arthur Guinness, whose hall they almost join. Tho bones aud fragments of monumental effigies so plentifully scattered about theso old places awaken deep Interest and speculations as to tbe lives and characters of those races long gone before. To the lover of natural beauty and quiet solemnity, I would say, visit Ivy lemon? Pass, the group of mountains called the Twelve Pins, ascend the one called Mul Rhea, and he will gain as tinea view of mountain scenery as can bo viewed in Ireland The Sun Betting behind the mountains skirting Klllery Bay, which la the autumn are covered with the heather bloom, gilds tbe whole scene with surpassing splendour. But I must close. It any brother reader would wish to visit these scenes and many others iu the Western Highlands, and will correspond with me, I shall be most happy to give him any information as to the route, and other incidental mutter«.
F. Harwood, 33, Newark-street, Leicester.
The percussion turbine, exhibited by Mr. Kelly, CK., the invention of Mr. Cheetham, of. Manchester, is quite a centre of attraction, lui great beauty is its simplicity—nothing to break, and nothing to wear except the axle. 1 have no doubt it will be heard more of.
Tbe Pneumatic Loom of Mouland and Coulong is particularly worth notice : It docs away with picking levers', bowles, peckers, straps, aod all these troublesome affairs, and works so smoothly and noiselessly that 100 of them In a shop would not make as much noise as an ordinary sewing machine. A pair of vertical engines combined by Atesare. Coatee, occupy a prominent position; they seem to work well. Mr. McCreery exhibits his celebrated spinning wheel, «o many of which he has mado for the Royal Family and the nobility. It is presided over by a merry old lady, who, with nimble Anger« and ready repartee, delights an admiring audience, one of whom made the remark that the wheel worked very quickly. "Is it any wonder" she says; " listen to tbo fine music she has." "Why? what effect has that upon her?" Is asked— "Just" says the old woman," she's (the wheel) like nil other jennies" it puts her clean mod.
A revolving shutter for shop windows or bookcases is well worthy of attention, aud will no doubt cone Into notice. The Imitation bronze statue« of Holland are very handsome.
BELFAST WORKMEN'S EXHIBITION.
Sir,—I herewith send a detailed account la three copies of the Belfast Noes letter of the Workmen's Exhibition now open in Belfast. The exhibition is very well worth я visit, aud many hours could be profltably spent there in examining the various ingenious products of tbe worklug man's brain. This item from я provincial town of Ireland augurs well for the success of the main exhibition to be shortly opened in London. Two or three turbine wheels are here at work; In fact, the motive power of the machinery section is given by a turbine made by the eminent engineers, Messrs. McAdaui Bros. Soho Foundry, Belfast; they hnve long been successful maker« of these water engines, having devoted particular attention to their manufacture for iorae years past.
TRADE AND COMMERCE. StR,—Your correspondent "Herbert," writes on these important subjects with a pithiness which Is almost convincing. He states that the balance of Imports over exports represent« the profit of a nation. aud illustrates it by an imaginary ship, which, sailing with Hlêfi.iO worth of goods, returns luden with £20,000 worth. Here is something for the consideration of our ministers and merchants. Let the Government nt once prohibit expertation—all that we import will then be clear profit. Let our merchants send forth their ships empty; tbe merchandise with which they return will then be so much to the good. But, unfortunately, there is a little flaw in the argument. Your correspondent's assumption would bo perlectly correct , if the trade were carried on by barter only, but this is not the case; we might cease to export, and yet, for a time, continue to Import as much as ever.
The subject of trading with foreign countries Is one of vital importance to the working man, and is not to be settled by a rash conclusion, or even by asking, as one of our Cabinet Ministère did, "Why should we refuse to buy cheaply from foreign countries, because they refuse to buy cheaply from ue?" The answer to this is, that by doing so we pay the wages of the foreign workineu, who make these cheap goods, aud therefore there is j ust «o much the less for our own workmen. When tbe amount becomes considerable, as it Is at the present time, our men are compelled to emigrate lu large numbers. It Is pretty plain that for each foreign workman wo support in this manner, one English workman is compelled to leave his country, or to become a pauper.
The whole subject is too vast and too Important to admit of proper discussion in the limited space you can devote to it. My only object in writing, is to point out what I believe to be an error in your correspondent's reasoning, and to caution your readers that я subject which offers so many points for consideration, cannot be settled by pithy sentence« or specious questions.
F. W. M.
DEW CAPS FOR REFLECTORS AND u' BOOTIS'
Sir,—In answer to " Hugo," I must say, that in the cool winter evenings, and indeed on most nights when a deposit of dew occurs on the tube, and when tbe telescope has been an hour and more in use, he will find a dew cap imperative. My tube has aa aperture of Hin., and I find а cap extending to 1ft. beyond the prism, is generally required on dewy nights, although many nights (as at the present timo), do occur when the prism may be exposed for a long time. Inside, and at the upper end of my cap, I have placed a ledge, for the lodgement of a series of tin stops, wbich vary the aperture from 10 to 7iu. Before I used a dew cap, I frequently had to remove the prism, warm and dry It before the lire, replace and readjust It. all this took up too much time. In using even a 4in. refractor, I • find a cap 8in. long absolutely necessary.
For the information of " U. A. C," during the present season, I have found /i- Boot!« well divided with loin. of aperture, and achromatic power of 300, the same with 9in-, but with »tin. aud same power, tbe discs *; were in contact; with Huyghenlan eye-piece, of about! ЗаО, the discs were split. At the same time, 1 found a of С Cancri welt divided, with apertures down to 9in and the same powers, but could not split it with any power of 8| luches, mainly owing, I suppose, to the > components of а ц Cancri being of greater magni tude than those of "' Boiitis, although their distanoe is eomewbat greater.
M. W. B. Coclcher. Downham Market.
Sir,—If "Vlvi» Sperandum" got я piece of wood, say ash or beech, Sin. square and 2ft. long, and steamed the middle of it well in я box, be coula bend it to the shape of outliue of boomerang, and leavo it till cold aad hard, nailed with a few cleats to я flat board ; then rip it lengthwise into five thicknesses of j each, or less, aud the grain of all would be the right way to resist fracture. Boomerangs used to be sold at the London . toy-shop« larger than his dimensions, and with cuds about square with each other. Thoee wo sec in the museums are frequently scarcely bent at all, and only a loot long, or a little more. Is his namo " Ylvis " or
"V,VU>? J. K.P.
DARK LINES Ш THE SOLAR 8PECTRUM. SIR,—I think Kirchhoff was quite right In his pre- i /erring what hi« spectroscope plainly taught him to■