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part of the matter forming a nebula is invisible, ■we remove the immense difficulty which we otherwise experience in attempting to conceive how nebulae have assumed or can retain their extraordinary shapes and yet be subject to the law of gravitation.

The researches of Muggins prove that many of the nebula) are gaseous self-luminons masses, whilst the spectra of others prove the existence of solid or liquid matter. These last being generally those which are most easily resolved, would be those which have been longest in existence, and which, therefore, should contain most liquid and solid matter.

The curious shapes of the nebula) are well explained on this theory.

Thus the spiral nebula? wonld bo produced by two masses of gas rushing together ai»d forming an eddy in whioh they become mingled with each other. If any detached portion of one gas got mixed up with the other gas, it would be drawn out by the eddy into an elongated spiral form, the earface of which would become visible by the light produced by the chemical action. This would be the kind of nebula which would be produced when the two masses of gas did not differ greatly in size, and rushed together in a line not very oblique to the line joining their centrei of gravity.

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Lussell

Some spiral nebn'te consist only of a single whirl. A nebula of this kind might be produced by a small mass of comparatively dense gas rushing obliquely into a large mass of rarer gas.* Such a mass would tend to the centre of Jgravity of :ho larger mass; and since tboso parts which are nearest the centre of gravity would be most accelerated, it wonld become drawn out into an elongated spiral form.

After a time the whole of the smaller mass of gas will have collected about the k centre, and a globular or planetary [nebula will be formed. #

In the annexed diagram, copied from a drawing by Lassell, we appear to have a globular nebula in the 'process of formation. That the smaller mass of gas has entered is shown by b of the

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obliquely ending

tubular portion is oblique to the axis of the tube; for the line a b will indicate the boundary of the larger mass. That the gas is collecting about the centre of the larger mass is indicated by the fact that the line o c joining the centre of the globe with the end of the tube is perpendicular to a J—as it should be, supposing the larger mass of a spherical form.

the fact that the

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J-iaDetary nebula;, consisting of more than one envelope might also be formed in the same way as those having only one envelope, the envelopes being formed in succession at different periods of time.

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Annular nebula) might be formed iu the following manner. If a small mass jof gas were attracted to a larger mass so Bb just to graze its snrface on passing it, its pBth (previously parabolic) would become elliptic, and its motion would be changed into a periodical revolution round the larger mass. At each revolution it would Lassell, pi. I. ng. 4. graze the surface of the larger mass, and the elliptic orbit would gradually be changed into a circular one. It would at length come to revolve about the larger mass in such a manner as continually to graze the surface, and an annular nebula would be the result.

Those nebula), like the larger one in Andromeda, in which streaks of darkness oross the bright parts, offer the greatest difficulty in their explanation.

We might imagine that a mass of rare gas has become entangled between two masses of dense gas, and that the masses of dense gas being attracted to one anothor, crush out the rare gas into a thin sheet, which, looked at edgewise, preserte the appearance of a dark streak.

Some of the nebulae of this kind have nuclei ; and it may be remarked that the position of the nucleus, which will be the centre of gravity of the nabula), is in the position in which we should expect to see it if the apparent vacuous streaks were in reality filled with matter.

Many of the nebula) are very much diffused, and in shape very irregular; but even these show certain characteristics which seem to indicate their mode of formation. The extreme faintnessof their light favours thehypothesis that they are not luminous throughout, bnt that their lumi

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JLosssll, pi. 5. fig. 21.

nosity occurs only here and there in comparatively thin shells. Again, if these nebnhc were luminous throughout, the intensity of their light should be greatest where the thicknoss of matter looked through is greatest, and should fade away at the boundaries, whereas, if the visible parts occurred in shells, the boundaries should appear brighter than other parts; for at the boundaries the line of sight would be very oblique to the shell, and a greater thickness of luminous matter wonld be looked through. Now if we examine any of the irregular nebulaa), we see some parts of it ending abruptly with a clearly-defined outline, whilst in other parts tbo light gradually fades away into darkness. We may suppose that in the one case we are looking edgewise at a shell, so that the line of sight is tangeutiul to its surface, whilst in the other case we are looking at a part where the luminous shell gradually thins out. Now in the first case we find that the light increases towards the border, consistently with the supposition that the visible parts are iu thin shells.

This peculiarity is, I apprehend, what Professor Bond and Mr. Lassell refer to when they speak of the scroll-like appearance of the nebula in Orion.

In those nebula) which appear to have assumed a more stable form, as in the elliptic and circular nebula), the light diminishes from the centre to the circumference.

These nebula) may be in a later stage of formation; they may have become more condensed, and a more intimate mixture of the gases may have taken place, and in consequence thev may be more or less luminous throughout. Their shape, and the fact that they are generally resolvable in the telescope, point to the conclusion Jthat they have been a long time in existence.

Before tnrning to the subject of oomets, I may remark that the theory that there are large masses of invisible gas traversing space, affords an explanation of the sudden temporary outbursts in the intensity of certain stars. Such an outburst might occur if a star became enveloped with a mass of gas with whioh it could chemically combine.

It also explains the phenomena of periodical stars. Mr. Huggins has found that the diminution in the intensity of the light of these stars is dne to an increase in the number and size of the absorption bands in their spectra.

It has already been suggested that large opaque bodies may be revolving in orbits round such stars, and periodically obscuring their light. We have only to suppose that large masses of invisible gas instead of opaque bodies revolve about them, to explain the phenomenon in accordance with spectroscopic observation.

(To be concluded next meeh.')

FRICTION IN STEAM CYLINDERS.*
By Mk. P. Jensen.

SO few data exist on the subject of friction in steam cylinders, that the author approaches it with some diffidence, more especially as he has not had time to make direct and comprehensive trials which wonld furnish particulars for exhaustive treatment of the subject. He, therefore, oan only offer such remarks and make such deductions from the experience of others and of himself that have a bearing on the subject, without assuming to settle questions relating thereto. Of the importance of the subject there can be no question, as engineers are awareofthegreat percentage of power that may be consumed in piston friction. Heno it is well to define this loss under various circumstances, and then to apply remedies for diminisTiing the loss. Friction in the steam cylinder may be classed under three heads; piston friction, slide valve friction, and stuffing box friction. As regards piston friction it ought to depend upon the working pressure, the packing material employed for keeping the piston tight, the extent of the rubbing surface of the packing, and the means of lubrication. It is evident that a piston should not be made to stand a higher pressure than that it is intended to work with, otherwise a great amount of power may be lost by unnecessary friction, and wear and tear both of piston and cylinder will ensue. It also appears evident that engines expanding the steam to any great extent in one cylinder should have piston packing, the tension of which is dependent upon and constantly varying with the pressure of the steam at any part of the stroke. There is not, it Is believed, any dilficuky in this, and all are doubtless familiar with oae or more constructions of pistons of this sort which answer the purpose in a greater or less degree.

The common rough and ready way of calculating piston friction by assuming a certain constant pressure per square inch of piston as being the measure lor the piston friction (which, as will be seen presently, constitutes by far the greater portion of the total friction) of the engine itself is erroneous, or at any rate should be used with discrimination. Although it has been found in a few instances that the friction of a piston for instance in an engine working with 2.J atmospheres may be expressed by (say) 21b. per square inch of the piston, which may or may not mean that the piston packing has had just the requisite amount of tension, and not perhaps 50 per cent, more than requisite, we have no right to infer that the same rule holds good with 5 or 10 atmospheres pressure. If the piston packing has just the right tension, the friction must amount to a certain percentage of the pressure. But we must not lose sight of another circumstance—namely, that the circumference of a piston increases as the diameter simply, while the area increases as the square of the diameter.

Ths question is, has a piston of 24in. diameter double the amount of friction, or has it four times the amount of that of a 12in. piston, other circumstances being alike, that is, with the same material, same depth of packing, state of lubrication, pressure, &c. We must not forget either that tho proportionate depth of packing varies with the diameter of the cylinder. Whether it is supposed to give less wear on the piston rings (an opinion considered incorrect by the author) or not, we need not stop to discuss ; tho practice is, however, not to increase the depth in direct proportion as

* Read before the Society of Engineers, Karen 7, 1869.

tho diameter of the piston increases in size, and thus it is that the piston friction does not in practice decrease in the ratio otherwise anticipated, though it is believed that it does decrease. In other words, it is propounded that piston friction us percentage of power decreases asdiameter increases, lint increases as pressure and depth of packing increase, the packing material being the same. In practice the following rule holds good :—Depth of packing = } >/<f in inches : for instance, for a lOin. cylinder, depth of packing = J X 7 = 6J; for smaller engines, $'*/Vd (say) 16in. cylinder, depth of packing = I X 4 = 2Jin. This is for east-iron packing rings. With Ramsbottom's steel ringsa much smaller depth is found quite sufficient. Hence if it is found that 21b. per square inch is the measure of the piston friction in a 12in. cy linler, it would seem that the friction of a 24in. cylinder (having fonr times the area bnt only double the diameter), would only he double, bnt ns tho depth of packing is as 23 to 389 it would 8-89

become X 2 = 3-38, so that the pressure per

23 square inchabsorbedbypistonfriction would become 3-38

2 x = 1091b. per square inch in a. 24in.

4 cylinder, and 21b. in a lGin. This is of course assuming the ordinary theory of piston friction to be corroot, namely, that it is to be calculated by the superficial area of tho piston packing x the pressure of the steam X the friction, co-efficient. If, then, the above be correct, it is dear that we must avoid taking a certain fixed percentage of the pressure on tho piston area as the measure of the piston friction, except we take the size of the cylinder into account.

Tho packing material has considerable influneco on the friction. Hemp packing for moderate and for high pressure causes more friction than metallic packing, which is now almost universally adopted. Cast-iron rings or Ramsbottom's steel rings, though not giving so little friction as gun metal, are generally preferred, because they wear well and aro not so much affected by grit. The author's experience is that Ramsbottom's rings are tight, wear well, and do not require excessivo tension. For great expansion in a single cylinder the tension of the packing should he dependent npon the varying pressure in the cylinder, as before stated.

In considering the question of stuffing box friction, the author would fi rst observe that the amount of los3 caused by it is only trifling if the packing is in proper condition and the gland has been properly fitted; but otherwise this loss may become enormous. The author is not aware of any comparative experiments showing the friction caused by the employment of various kinds of stuffing-box packing, although that, doubtless, has also a great influence. But what all are aware of is the great wear on tho piston rod through having the packing too hard. A careful engine driver avoid this, but every engine driver is not carefnl, and if he has many other things to look to, as is often the case, then the plain question -^ysaajiljetljer it is not better either to use a packing tKat requires but little lubrication, or else to provide means for keeping the packing continuously supplied with a very Blight amount of grease, which, as experience has shown, can be effected by greasing the Bteam before entering the cylinder. No other means are then found necessary for lubricating the slide rod or piston rod, and hard packings become an impossibility.

It is not intended to describe the various kinds of packing; suffice it to say that there are some which answer their purpose very well, some of them requiring little or no lubrication. The selflubricating mineral packing has under some circumstances answered very well. Metallic stuffing box packing has been proposed and used. On account, however, of the great depths required and the expense and trouble attending its manufacture, it has never come into extensive use. Metallic stuffing-box packing would be a great boon, provided it answered its purpose. Mr. John l'cnn used to have one of his small shop engines fitted with metallic stuffing box packing, and the author believes he has so now.

(To be continued.)

The VIelle-Montngae Zinc Mines and Fonndrios Company increased its production of zinc last year to 43,016 tons, as compared with 40,210 tons In 1808, SO.zoo ton* In 1*67, 81,724 tons in 1S68, and 80.C92 tons in 1865.

HINTS ON THE SELECTION AND USE OF A MICROSCOPE.

THE quality of a microscope, says the Technologist, of course depends entirely upon the perfection with which it shows objects as they really are. Some microscopes distort objects so ns to give views that are anything but correct. Others colour whatever they show with all the brilliant hues of the rainbow. We have often admired the magnificent colours displayed by natural objects under the microscope, such, for example, as the petal of the geranium, whose cells are tilled with the most brilliant scarlet colouring matter: or the crystals of the ruby oxide of copper, which are gorgeous beyond expression ; or various objects seen by polarised light, which gives to some of the most colourless and transparent crystals colours that far excel the tints of the ruby or the sapphire; but we have often smiled when asked to view the splendid colour shown by hair, or a fly's eye, or a section of wood seen by ordinary transmitted light, for we well knew that these objects have no colour of their own, or at least only dull, neutral tints, and that all the gorgeous hues so lavishly displayed wero merely the result of defects in tho microscope.

It is unquestionably true that one of the fine larga achromatic mioroscopes, furnished with objectives of low as well as high power, would be the best for all purposes of examination. But such microscopes are very expensive. A tolerable one cannot be had for less than one or two hundred dollars, while a first-class one will cost four or five times that amount. Snch a microscope, although desirable, is not absoln'cly necessary, and therefore we will turn our attention to the less costly kinds.

The first that presents itself is the simple lens mounted in a metal or horn frame. In the hands of a skilful observer, this instrument will do good service. Opticians frequently arrange several lenses in one frame, and suggest the idea of combining them so as to obtain an increase of power. In general, however, this idea is fallacious, and the instruments are not properly arranged for the purpose. In the first place, there is no diaphragm (or thin plate with a Bmall hole in it) between the lenses to cut off the extra light; and, in the second place, the lenses are placed ns close to each other as possible, so as to occupy but little room, and this prevents us from obtaining a good effect. Moreover, it is unfortunately true that opticians (somebody once called them in derision shoptieians) rarely give us the best selection of powers. Thcro is too much Bameoess in them. The be*t arrangement we could find in a large collection consisted of three lenses, whoso magnifying powers were respectively 25,20, and It! diameters. Now, this is not variety enough, and tho reason for not making a greater difference between tho powers of the lenses is the fact that high powers are so much smaller than the lower powers that to combine them in the same frame makes a clumsy instrument. We confess, however, that we would much prefer efficiency to elegance.

A frame containing three plano-convex lenses, lin., Jin., and iin. focus, we have found altogether the most convenient arrangement. The magnifying powors are 10, 20, and 40 diameters ; and whether we desire to examine a mineral, a flower, or an insect, whether we wish to look at the mildew on a grape-leaf or the beetle which preys upon tho buds, such a series of powers will enable ns to do so thoroughly.

In selecting single lenses to be used as microscops?, procure, if possible, those of which one side is perfectly flat, that is to say, plano-convex. The view obtained by snch lenses is always better than that given by donble convex lenses of the same power. Such simple mioroscopes aro undoubtedly the best cheap instruments. But at a very slightly higher cost we may obtain that best of all simple microscopes—Wollaston's doublet. This microscope is formed of two planoconvex lenses adjusted together in the same tube. It is rajcly that we can find a good one in the opticians' stores, but they are so easily mounted ihat auy working optician could put one together at short notice. One of our friends made a remarkably efficient instrument of this kind, having formed the lenses of plate glass (a piece of broken store window), which consequently did not require the piano side to be ground, and arranged the lenses in a tube made of stout writing-paper, pasted. Suitable lenses could, no donbt, be procured by mail from most opticians, and it would no doubt require no great manual dexterity to mount them.

ON THE RELATIONS BETWEEN BODY

AND MIND."

Lectube II.

(Continued from page 243.)

IT is a natural question. Whence come thoao animal traiU and instincts in man 1 Wbenc e was derived the instinct which taught the idiot woman to gnaw through the umbilical cord? Was. it really the reappearance of a primitive instinct of animal nature—a faint echo from a far distant past testifying to a kinship which man has almo*t outgrown, or has grown too prond to acknowledge? No doubt such animal traits are marks of extreme human degeneracy, but it is no explanation to call them so ; degenerations come by law, and are annatural as natural law can make them. Instead of passing them by as abnormal, or, worse still, stigmatising them as unnatural, it behoves us toseek for the scientific interpretation which they must certainly have. When we reflect that every human brain does, in the course of its development, pass through the same stages as the brain* of other vertebrate animals, and tint its transitional states resemble the permanent forms of their brains; and when we reflect further, that the stages of its development in the womb may be considered the abstract and brief chroniole of a series of developments that have gone on through oountlcss ages in nature, it docs not seem so wonderful, as at the first blush it might Jo, that it should, when in a condition of arrested development, sometimes display animal instincts. Summing up, as it were, in itself the leading forms of the vertebrate type, there is truly a brute brain within the man's ; and when the latter stops short of its characteristic developement as human —when it remains arrested at or below the level of an orang'e brain, it may be presumed that it will manifest its most primitive functions, and no higher functions.

I am not aware of any other considerations than those just adduced which offer even the glimpse of an explanation of the origin of these animal traits in man. We need not, however, confine our attention to idiots only. Whenoe come the savage snarl, the destructive disposition, the obscene language, the wild howl, the offensivo habits, displayed by some of the insane? Why should a human being deprived of his reason ever become so brutal in character as some do, unless he has tho brute nature within him? In most large asylums there is one, or more than one, example of a demented person who truly ruminates : bolting his food rapidly, he retires afterwards to a corner, where at his leisure he quietly brings it up again into the mouth and masticates it as the cow does. I should take up a long time if I were to enumerate the vurious brute-like characteristics that aro at times witnessed amoDg the insane; enough to say that some very strong facts and arguments in support of Mr. Darwin's views might be drawn from the field of morbid psychology. We may, without much difficulty, trace savagery in civilisation, as we can trace animalism in savagery; and in the defeneration of insanity, in the unkhiding, so to say, of the hnman kind, there are exhibited marks denoting the elementary instincts of its composition.

It behoves ns, as scientific inquirers, to realise distinctly tho physical meaning of the progress of human intelligence from generation to generation. What structural differences in the brain are implied by it? That an increasing purpose runs through the ages, and that " the thoughts of men are widening with the process of the suns," no one will call in question ; and that this process has been accompanied by a progressive development of the cerebral hemispheres, the convolutions of which have increased in size, number, and complexity, will hardly now be disputed. Whether tho fragments of ancient human crania which have been discovered in Europe do or do not testify to the existence of a barbarons race that disappeared before historical time, they certainly mark a race not higher than the lowest surviving human variety. Dr. Priehard's comparison of the skulls of the same nation at different periods of its history led him to the conclusion that the present inhabitants of Britain," either as the result of many ages of great intellectual cultivation, or from some other cause, have much more capacious brain-cases than their forefathers.-' Yet stronger evidence of a growth of brain with the growth of intelligence is furnished by an cxami

• Two lectures delivered at the Royal Collage of Physicians In 1870. By rtEiiRT Macdslkt, H.D., F.K.C.P., Professor of Medical Jurisorudenoo In University College, Loudon.

nation of the brains of existing savages. Gratiolet has figured and described the brains of the Hottentot Venns, who was nowise an idiot. He found a striking simplicity and a regular arrangement ef the convolutions of ths frontal lobes, which presented an almost perfect symmetry in the two hemispheres,;involnntorily recalling the regularity and symmetry of the cerebral convolutions in the lower animals. The brain was palpably inferior to that of a normally developed white woman, and could only be compared with tho brain of a white idiotic from arrest of cerebral development. Mr. Marshall has also recently examined the brain of a Bushwomnn, and has discovered like evidence of structural inferiority: the primary convolutions, although all present, were smaller and nmch less complicated than in the European ; external connecting convolutions were still more remarkably defective ; the secondary Bulci and convolutions were everywhere decidedly less developed ; there was a deficiency of transverse commissural fibres j and inBize, aud every one of the signs of comparitive inferiority, "it leaned, as it were, to the higher quadrum»nons forms." The developmental differences between this brain and the brain of a European were in fact of the same kind as, though less in degree than, those between the brain of an ape and that of man. Among Europeans the average weight of the brain is greater in educated than in uneducated persons ;its size—other cirenmstanoes being equal—bearing a general relation to the mental power of the individual. Dr. Thurnamconcludes, from a series of carefully -compiled tablos, that while the avernge weight of the brain in ordinary Europeans is 49 ounces, it is 546 ounces in distinguished men; and Professor Wagner found a remarkably complex arrangement of the convolutions in the brains of five very eminent men which he examined. Thus, then, while we take it to be well established that the convolutions of tliehuman brain have undergone a considerable development through the ages, we may no less justly conclude that its larger, more numerous, and complex convolutions reproduce the higher and more varied mental activity to the progressive evolution of which their progressive increase has answered—that they manifest the kind of function which has determined the structure. The vesicular neurino has increased in quantity and in quality, and the function of the increased and more highly-endowed structure is to display that intelligence which it unconsciously embodies. The native Australian, who is one of the lowest existing savages, has no words in his language toexpress such exalted ideas as justice, love, virtue mercy; he has no snch ideas iu his mind, and cannot comprehend them. The vesicular nenrine which should embody them in its constitution and manifest them in all its function, has not been developed in his convolutions; he is as Incapable, therefore, of the higher mental displays of abstract reasoning and moral feeling as an idiot is, and for a like reason. Indeed, were we to imagine a person born in this country, at this time, with a brain of no higher development than the brain of an Australian savage or a Bushman, it is perfectly certain that he would be more or less of an imbecile. Aud tho only way, I suppose, in which beings of so low an order of development could be raised to a civilised level of feeling and thought would be by cultivation continued throngh several generations ; they wonld have to undergo a gradual process of hnmanisation before they could attain to the capacity of civilisation.

Seme who one moment own freely the broad truth that all mental manifestations take place through the brain, goon, nevertheless, to straightway deny that the conscience or moral sensibility can be a function of organisation. But if all mental operations are not in this world equally functions of organisation, I know not what warrant we have for declaring any to be so. The solution of the much-vexed question concerning the origin of the moral sense seems to lie in the considerations just adduced. Are not, indeeJ, our moral intuitions results of the operation of the fundamental law of nervous organisation by which that which is consciously acquired becomes an unconscious endowment, and i3 then transmitted as more or less of an instinct to the next generation? Thev are examples of knowledge which has been hardly gained throngh the suffering and experience of the race being now inherited as a natural or instinctive sensibility of the well-eonstituted brain of the individual In the matter of our moral fecliugs we are most

truly the heire of the oges. Take the moral I sense, and examine the actions which it s motions I and those which it forbids, and thus analyse, or, as it were, decompose, its nature, and it will bu | found that tho actions which it sanctions arc those which miy be proved by sober reason to be conducive to the well-being and the progress of | tho race, and that its prohibitions fall upon the actions whioh, if freely indulged in, would lead to the degeneration, if not extinction, of mankind.' And if wo could imagine tho human race to live back again to its earliest infancy—to go backwards through all the scones and experiences through which it has gone forward to its present height—and to give back from its miuJ and character at each time and circumstance, as it passed it, exactly that which it gained when it was thore before,—should we not find the fr.igmonts and exuviaj of the moral sense lyin^ here and there along the retrogido path, aud a condition at the beginning which, whothur simian or human, was bare of all true moral feeling?

Wo are daily witnesses of, and our daily aotions testify to, tho operation of that plastic law of nervous organisation by which separate and successive acquisitions are combined and so intimately blended as to constitute apparently a single and undecomposablo faculty: we observe it in the formation of our volitions; and we observe it, in a more simple and less disputable form, in the way in which combinations of movements that have been slowly formed by practice are effected finally as easily as if they were a single and simple movement. If the moral sense —which is derived, then, insomuoh as it has boon acquired in the prooess of human development through the ages—were not more or less innate in the well-born individual of this age, if he were obliged to go, as tho generations of his forefathers have (tone, through the elementary prooess of acquiring it, he would be very much in the position of a person who, on eaoh occasion of writing his name, had to go through the elementary steps of learning to do so. The progressive evolution of the human brain is a proof that we do inherit as a natural endowment the laboured acquisitions of our anoestors; the addod structure represents, as it were, the embodied experience and memories of the race; and there is no greater difficulty in believing that the moral sense may have been so formed, that in believing, what his long been known and is admitted on all hands, that the young fox or young dog inherits as an instinct the special cunning which tho foxes ami the dogs that have gone before it have had to win by hard experience.

These remarks are not an unnecessary digression. Nor will they have boon made iu vaiu if they serve to fix in our minds tho conviction that the law of progressive evolution and specialisation of nerve-centres, which may bo traced generally from tho first appearance of nervotlssno in the lowest animals to tho complex struoturo of the nervous system of man, and specially from tho rudimentary appearance of cerebral convolutions to the numerous and complex convolutions of the human brain, does not abruptly cease its action at the vesicular uenrine of the hemispheres, but continues in force within the intimate recesses of the mental organisation. Moreover, they are specially to the purpose, seeing that they enable us to understand in some sort now it is that a perversion or destruction of tho moral sense is often one of the earliest symptoms of mental derangement: as tho latest and most exquisite product of mental organisation, the highest bloom of culture, it is tho first to testify to disorder of the mindcentres. Not that wo can detect any structural change in such case; it is fur too dolicate for that. Tho wonder would, indeed, bo if we could discover such more than microscopical changes with the instruments of research whioh wo yet possess. Wo might almost as well look to discover the anatomy of a guat with a teloscope.

(7b be contimtvd.)

GRINDING EDGE TOOLS.

EDGE tools are fitted up by grinding, very much as a plank would bo reduced iu thickness were a large plane employed, in which were set a hundred or more very small gouges, each cutting a narrow groove. The sharp grit of the grindstone being harder than the iron or steel, cuts very small channels iu the surface of the metal, and tho revolving disc carries away all tho minute particles that arc detached by the grit.

If we were to examine the surface of a tool that has just been removed from a grindstone, under the lenses of a powerful microscope, it would appear, as it were, like the rough surface of a field which has recently been scarified with some implement which formed alternate ridges and furrows. Hence, as these ridges and furrows run together from both sides, at the cutting edge, the newly-ground edge seems to be formed of a system of minute teeth, rather than to consist of a smooth odge. For this reason, a tool is first ground on a coarse stone, so as to wear the surface of the steel away rapidly; then it is polished on a wheel of much finer grit; and finally, iu order to reduce tho sorrat-ure as much as possible, a whetstono of the finest grit must be employed. This gives a cutting edge having the smallest possible serration. A razor, for example, does not have a perfect cutting edge, as one may perceive by viewing it through a microscope. And yet the serrations are actually so much smaller than a human hair that the minute teeth cut the hair in twain j but when the serrations on. tho edje of the razor becomes so battered up and dull that they will not sevor a hair, or cut a man's beard off, the edge must bo houed and strapped until the system of minute teeth will be so much smaller than a hair that several of them will take hold of the smallest hair at ouoe. These suggestions will furnish somothing of an idea of the operation in grinding and whetting edge tools.

Beginners are sometimes instructed, when grinding edge tools, to have the stone revolve towards the cutting edge, and sometimes from it. When the first grinding is being done it is a matter of indifference whether this is done or not; but when the finishing touches are applied near and at the very edge, a grinder can always comptete his task with more accuracy if the periphery of the grindstone revolves towards the cutting edge, as the steel that is worn away will be removed more easily; whereas, when a stone runs in the opposite direction, the grinder cannot always toll exactly when the side of the tool is fully ground up to the edge. This is more especially true when the steel has a rather low or soft temper. Tho stono, when running from the edge, will not sweep away every particle of tho metal that hangs as a "feather;" but when the stone revolves towards the edge there will be no "feather odge " to deceivo tho eye of tho grinder.

WATSON'S DEE1* TCMJLAli WELLS. (Illustrated on next page.)

THE advantages claimed for Mr. Watson's system of obtaining water or other fluids from any depth, over any other method, will be easily understood by our sciontilic readers from tho accompanying cuts, with but little explanation of the details; its utility in boring through a hard or rocky soil being more particularly prominent.

In sinking or boring by this method, in ordinary cases, the first length of tubing is provided with a (luted stool penetrator, having a groove cut in the part fitting into the tube, so as to allow it to revolve on the screws in the lower end of the pipe, which is made stronger for the purpose. The spindle for carrying the weights used in driving down is provided with a collar, tho lower side of which forms a fair surface to fall on to the brass hand nnt, which is screwed on to the upper end of the tube, so that it is not injured by the blow, and when down to the snrfaoe of the soil this nut is removed and another length of tube connected with an ordinary socket joint, as shown i nthe cnt, tho process being continued as before, and tubes added as required. Iu boring through a rocky Boil a double tube is used; the outer tube at its lower end has a steel collar fluted on the outside, aud also revolving at each blow of tho weights in a similar manner to that in the foregoing.

The inner ube is provided with a steel point likewise constructed to revolve, as in the first instance of the single penetrator, but has, in addition, two recesses to suit the two catches or tumblers fitted iu the revolving collar of tho outer tube, which keep it in its prober position, without impeding its withdrawal when necessary. The two tub-js are of equal lengths, fitted with brass hand-nuts at the upper ends, similar to that on the singlo tube, thus insuring their being driven equally together. The inner tube can be drawn to the surface at any time, cither for tho purpose of being sharpened, or of ascertaining the nature of the soil, &c, and ropluced with perfect case ; but in tubes of Sin. or more in diameter, provisioncun

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be made for ascertaining the nature of the vaiions strata the tube is parsing through without removing the inner tube at all. Where the outer tube is found to beat a sufficient depth to insure a good supply of water, the inner tube is withdrawn. The valves, pump, bucket, und gear arc then placed in position—usually about 20ft. from the surface of the water—the pump rod being made hollow, so that in the event of grit or saud interfering with the proper working of the valves water can be passed down it on to them, and the obstruction cleared away—though this will be hut seldom required, the pump btiug provided with a head valve, which always retains a column of water after it is discharged by the pump bucket. The whole of this arrangement will be clearly understood from the engraving, it being a very compact and serviceable job.

These wells arc well adapted for the colonies,

tropical climates, farms, gold and other mines,

also in testing for mineral and other substances,

ayjSMTll used to advuntage as boring tools in

a^artesian well making.

For mansions situate at any distance from the water the tube wells are found useful.

These pumps are now being constructed for tho patentee, Mr. G. Watson, nf PlaistoWjby Messrs. T. Blundell and Sons, of West India-road, Limehouse.

THE " PHANTOM" BICYCLE.
(For Illustration see page 277).

TflB machine represented in the accompanying sketch has been the subject of no little controversy union; some of our readers, and in placing this cut before them we would recommend those who may desire to have further particulars than we can afford space enough to convey to consult the pages of the interesting pamphlet," The Bicycle ; or, the Wheel and the Way,"from which we make the following extracts:—

"The machine is steered from the middle of the frame, or

from both wheels, nnd not fiom the front wheel alone, as in 'lit- ordinary bicycle, aud as the front wheel only turns half as much as usual, it is never brought into proximity even with the rider's thighs. It is completely railed off too by the frame within which it is enclosed. In turning a corner, or on a curve, each of the wheels are put upon the -.ma- arc of a circle; the b;ick wheel, therefore, always fvtUnct the line of the leading wheel; it passes over exactly the sume ground, in fact; there is in consequence no 'drag.' In the event of a fall the rider does not get hurt by the machine—that is, he cannot get * mixed up ' or entangled in a painful way between the front wheel and the backbone, as in the ordinary bicycle. The shape of the framework ensures greater speed being obtained than does that of the ordinary pattern. There are very convenient * steps' fur mounting and dismounting, aud the same contrivances are serviceable as safe and comfortable rests for the feet. A spring concealed in the steering-socket destroys the vibratory concussions usually conveyed to the hands. The cranks are readily adjustable to any length of throw, and when 'adjusted' they do not work loose. Both the wheels have fixed axles, and run in gun-metal bearings provided with separate oil cups which do not leak. Lastly, the wheels are a grand improvement in themselves, being made upon the suspended principle in such a way that they act as springs, and assist in dispelling the concussious caused by rough roads. The general result is that a bicycle is produced which is of a decidedly improved appearance, which is much safer to ride, easier to Bteer, far less dangerous to full from, and which is much easier to mount and dismount. Finally, the speed, miJ consequently the case of driving are improved by at least athiid."

The remarks as to india-rubber tires are of general interest■—

"A rubber tire is usually made up smaller than the rim of the wheel it is intended for, aud is held in its place by being stretched into a groove, brmed in the wheel by putting flanges on e;ich side of the rim. The defects of this plan are that when the wheel is pivoted upon its base, as when the machine is turning a corner, the rubber tire is wrung or twisted by the screwing motion of the wheel upon the ground, and directly a part of it is raised a little above the edge of the llange, the whole of the tire instantly springs out of the groove. To get it back is a job of some difficulty, especially if the accident happens when on a journey, us it takes at least two or three pairs of hands, and some little skill to stretch it in again. The stretchingou of the tire is intended to prevent it from being twisted out by making it impossible to stretch it further. This plan not only frequently f;ils to effect its object in that respect, however, but it exposes the tire to a constant daugcr of, if possible, a worse kind in another way. Stretched rubber gapej wherever it is cut, and as a very few

weeks* wear, especially iu districts wherethc roads are macadamised, produces a good many cuts in the tire, the result is that it is disfigured by a number of ugly Raps, and is drawn up into thick and thin places, instead of being of an even thickness throughout its circumference. It then makes tha machine bump and down, and becomes more of a nuisance than an advantage, and hv-and-bye the contractile tendency is strong enough in the thick parts to tear the tire completely asunder at one or other of the thin places.

"The rubber tire of the 'Phantom' is a different thing-, however, and it is not liable to any of these disadvantages. The principle upon which the wheel is constructed 'dispense* altogether with the necessity for an iron tire to keep it together, as the rim is held in by the suspending rods; that leaves a wood surface upon which to fix the mbber tire. The latter is made half round, and has a canvas base made up with it in the vulcanising process. The canvas base serves two purposes; it prevents the tire from stretching in ther direction of its length, and it forms a bed for holding the heads of short iron pins, which are driven through the rubber and into the wood rim at intervals of about every inch of the circumference. The heads of these pins are buried in therubber, which closes over the hole made in driving them in, so thai they are not seen or felt in any way. They keep the rubber tire from being shoved off. Then, as the rubber is not, and in fact cannot be, stretched in the direction of its length, it does not gspc aud stretch wherever it happens to get cut by sharp atones. Consequently there is practically no end to the wear of the tire, as, in spite of the cnts it may have across it, it retains its uniformity of thickness, and there is never any defect in its action. Of course the cutting of trie rubber tire cannot be prevented, bat by this plan of fixing it on, the practical usefulness and luxurious effect is not diminished by the cutting, the gaping of the cuts being entirely prevented."

TO CLEAN PAINT.—There Is a very simple method to clean pnfnt that bus become dirty, and it our housewives should adopt it, It would t>ave them a great deal of trouble. Provide a plate with some of the best whitiug to be had, and have ready some clean warm water and a piece of flannel, which dip into the water and squeeze nearly dry; then take as much whiting as will adhere to it, apply it to the painted surface, when a little rubbing will instantly remove any dirt or grease. After which, wash the part well with deal] water, rubbing it dry with a soft chamois. Paint thus cleaued looks as well as when first laid on, without nuy injury to the most delicate colours. It is lar better than using soap, and does not require mure than half the time aud labour.

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LETTERS TO THE EDITOR.

f We do not hold ourselves responsible for the opinions of our correspondents. The Editor respectfully requests that all communications should be drawn up as briefly as possible.]

♦.* All communications should be addressed to the Editor of the KNGLian Mechanic, 31, Tavistockstreet, Coveni Garden, >V.C.

All sheques and Post Office Orders to be made payable to J. Tassmobe Edwards.

ASTRONOMICAL, OPTICAL, AND GENERAL.

SIR_Lotnie,ii«-j)rii;iM. congratulate my fellow subscribers upon the advent into your columns of our Great Solar Spectioscopist, Mr. J Noiman Lockyer. Let us hope that after the appearance of so convincing a reply from the man, perhaps of all living the best qualified to speak ex cathedrd on this special subject, we shall have no more vague guesses and expressions of doubt from people who are confessedly ignorant of the very elements of the problem which they undertake to discuss.

Lower on the same page (256), I find two or three queries by Mr. B. W. Bishop, towhlch I will reply in order. First, then, just as twilight is fading, is the most favourable time to examine the colour of a star. In the case of a star like Sirius, Mr. B. must remember that from its relative proximity to the horizon, atmospheric dispersion operates in tinging It very perceptibly with colour; and th's Is exaggerated by Its projection i. the block background of the midnight sky. Of course, I am supposing the star to be one of a tolerably low magnitude. Some of the minute red stars require the darkest sky you can get, and some

little attention to boot, to discern their colour fairly. On the other hand, that lovely pair a Herculifl is never seen to snch advantage as lu full twilight. I must confess my Inability to " give the comparative brightness of the chief nebula visible in a 3in. achromatic," because I am unaware of any photometric process which Is applicable to such a measurement: but If a rough eye estimation of relative visibility be of any use to your correspondent, I may tell him that of the nebuln now favourably situated for observation, he ought to see 70 Hersch. I. Vlrgiuls, and will have some difficulty with 99 Hersch. 1 Bootls; while 418 Bench. II. Bootis,and 756 Hersch. II. Bootls will be beyond his power altogether. 13 Messier Herculis he will either barely resolve, or see as a bright nebula, according to the excellence of his instrument. 57 Messier, the Ring Nebula in Lyra, will, in a first rate instrument, show traces of luminosity inside of the ring proper. This is all vague enough, but I do not see well how to frame my response differently. Before disclosing this branch of my subject, I may say

NEW STYLE Of RAILWAY.

that June Is, as my querist probably knows, the worst month of all the twelve for the examination of neuulse.

I may tell "Investigator" (also on p. '256) that the method now usiversally employed, where practicable, for the determination of longitude, is that by the Electrlo Telegraph. As he appears to possess •• Loomiss Practical Astronomy," I can refer lilm to pp 3 '5, tt art-, of that work for full details of the method adopted In practice. It may, however, serve to show with what extraordinary accuracy longitude can be obtained by the transport of chronometers. If I mention that of Mr. Airy, in 1814, superintended the transmission of thirty pocket chronometers ten times backwards and forward between Greenwich aud Feagh Main at Valencia, In tho extreme West of Ireland; and that when the difference of longitude betweeu these two places was redetermined galvaulcally In the summer of 1863, the result was almost precisely Identical with

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THE " PHANTOM " BICYCLE—(Described on page 276.)

that obtained by the older method. Moon Culminating Stars, unless observations be very much multiplied and great care be taken to observe both limbs of the moon, give but lndiffereut results, and Lunardistanccs, even in the bands of skilled observers, ore only pretty good; but Occultatlonslof Fixed Starsiby the Moon when carefully observed, and rigidly reduced, are very much better still. Secondly, every visible Occultatlon Isobserved at Greenwich, as are tho phenomena of Jupiter's Satellites Ac. These ore published at Intervals lu the "Monthly Notices of tho Royal Astronomical Society"; and this answers your correspondent's third query as well. Next, all the observations at Greenwich of the Moon, both with the transit circle on the Meridian, and with the altazimuth off it, are "for the purpose of detecting errors of the lunar tables." The Greenwich observations are published by John Murray, of Albemarlestreet, Loudon. With regard to the Immediately following question, he may take the length of the Polar semi-axis of the Earth at 20853708ft., and that of the I equatorial semi-axis he may deduce from it by con

ceiving with the Astrouomer Royal that the el IIplicity amounts to 003352. I must, however, add that a most elaborate Berles of investigations, undertaken by Colonel Clarke, of the Engineers, tends to show that the ellipsoid which best represents existing measurements has its major axis (Equatorial) In Longitude 13° 58' 5'.E, aud that the greatest and least

1

values of the meridian compression are in lon

286779

1

gltude 13° 58' 5* E., aud in longitude 103° 58' 5' E

309364 The difference of the Equatoria' semi-axes is 5308ft. or, roughly, about a mile. It will hence be seen that the figure of the Earth Is by no means absolutely symmetrical, nor even that of any solid of revolution. Fiually, " Investigator's" references to page 130, &co are presumably te those of some volumof the "Nautical Ale manac," but, in the absence of the name of the work to which they pertain, they are just a little vague.

"The Welsh Shepherd," p. 256, like numberless other

people, severely exercises himself about a question upon which as much nonsense, physical and metaphysical, has been talked. as has been utteredt about most things. The whole matter seems to He In a nutshell. If, from the way our eyes are placed in the head, we have to raise them to look at a part of an object, we say that that is tke top ; If we have to depress them to see another part, we call that the bottom. Our whole notion of up and down is derived from motion; and if the lm age fell upon the stomach instead of tho retina, and we had to raise our body to perceive It, we should say that Hint part was tho highest; If, on the other band, the body had to be lowered, we should call the part of the image which necessitated such lowering for Its perception the lowest. The soculled " Inverted image" on the retina, is treated by most people as though, so to speak, we saw thit; albeit to do so, wo should have to have another eye behind it! _ _

What, In the name of fortune;does "F. W. M. (p. 257), imagine he is adding to a controversy which has beou carried on int<" a[1 »<""«"», by reiterating what has been said over and over and over again about, the Earth aud Moon forming parts of one solid globe?

Fellow Of The Roial Astronomical Sociktv.

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