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LETTERS TO THE EDITOR.

[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 ENGLISH MECHANIC, 81, Tavistock

street, Covent Garden, W.C.

I

ISOMETRICAL DRAWING.

[84] SIR,-In answer to "Isometros" and T. Smith,

send two photographs of the instrument I mentioned on page 381. The base-piece B is of sheet iron with the upper edge straight and bevelled off very thin, and with a gap in the middle of about 3 in. for the pencil to work round in Fig. 1. The base supports the exalong its edge, and also supports the pillars P P through panding crank C, which is graduated to 3in. diameter the tops of which the long sheet bar N S (15 in. long) slides. Under N S is another smaller steel bar E W, fixed accurately square with NS by being driven

CHEAP AND GOOD GAS.

[85] SIR,-"C. D. C." in your issue of July 1, No. 275, has contributed a letter on a means to obtain cheap and good gas, in which he has been betrayed into the conventional habit of abusing the gas companies, when in reality the fault is much oftener to be found on the side of the consumer. He says that when the gas the gas companies find it convenient to extract. If he leaves the retorts it is rich in carburetted vapour, which knows anything about the condition of gas when it leaves the retorts, he will readily admit he would not care about its being supplied to him in that state, and until some of the condensable matters and other things had been got rid of.

All Cheques and Post Office Orders to be made pay through holes in the shaped brass casting T. The I don't think he would find it more expedient to use it

able to J. PASSMORE EDWARDS.

"I would have every one write what he knows, and as much as he knows, but no more; and that not in this only, but in all other subjects: For such a person may have some particular knowledge and experience of the nature of such a person or such a fountain, that as to other things, knows no more than what everybody docs, and yet to keep a clutter with this little pittance of his, will undertake to write the whole body of physicks: a vice from whence great inconveniences derive their original."-Montaigne's Essays.

IMPROVED TRICYCLE.

[83] SIR,-For the benefit of those who are interested in velocipede construction, I send a photograph

FIC.I

pin of the crank which is held fast by the screw seen
over graduation 3 on the crank, works in a hole in the
shaped plate A A, which is slotted to take the pencil-
slide, and has also two brass bars to form another slide
fastened on by small screws, and this plate also has two
pillars P P which slide on the cross bar E W. Now,
postponing the consideration of the rest of the instru-
ment, suppose the crank to be "rotated," as the
Yankees say, it is clear that every point of the plate
will travel round in a circle, while the plate itself re-
mains always parallel to its original position as the
steel bars slide freely in every direction-N-S. E.W.,
and if the pencil were fastened anywhere in the slot it
would make on the paper underneath a circle of the
same radius as the crank is set to. Now instead of the
pencil being fixed in the slot, it is attached to the
middle part of the lever X Y (which is 4in. long) by
means of the large milled headed nut Z,
and the two ends of the lever X Y slide
respectively on the bar N S, and in the
slide A. Now suppose the crank to be
set going as before, it is clear that the
pencil will be carried from N towards S,
and back twice the length of the crank
C, and as the end X of the lever X Y
cannot move at all to or from E W, while
the other end Y of that same lever does
move East and West twice the length
of the crank C, therefore the pencil which
is attached somewhere between a and y
will move E. W. a distance proportioned
to how far Z is fixed away from Y. If Z
is in the middle, then the breadth of
the ellipse will be half the length, and
if Z is at .578 of the distance of Y
towards X, then the ellipses will be the
isometrical projections of circles, as that
is the decimal of

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the conjugate axis exactly cuts into a notch made in the
middle of the gap in the base-plate close to the centre
of the crank. Hold it firm and move the crank gently
round half a turn or a whole turn as necessary. I have not
tried, but should think that the mechanical arrange-

W

1 1.73. use the instrument is to set the crank to the length of the transverse axis of the ellipse required, and to lay the and brief description of a tricycle, which, in my feather-edge of the base plate B accurately down on opinion, possesses some little novelty and merit. It the line of the transverse axis, and to take care that belongs to a friend of mine, and has been used by him with great success for the last twelve months. As will be seen from the illustration, the single wheel behind is the driver, and the pair in front the steering ones. The frame or back, with spring and saddle, are almost identical, both in form and material, with those of the bicycle. It is worked by a pair of hand and foot levers, connected to a pair of 6in. cranks, at quarter centre. The crank axle is of steel, 8in. in length, and gin. in diameter. It is loose in the nave, so that the cranks are at rest in going down hill. A small ratchet wheel, 2in. in diameter, is fixed upon the end of nave, while the axle carries an arm and catch, which work the ratchet (see Fig. 2). The steering lever is rigidly fixed to the swivel pin of front axle; it is 21in. in length, and has a hob, 5in. across, which is acted upon by the knees of the rider. The swivel-pin and barrel in which it works are inclined away from the rider at an angle of 22 degrees; this throws the weight to the inside in turning, and so ensures perfect safety in passing sharp curves. The wheels are 30in. in

FIG.

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diameter all round; the driving one is hooped with
iron, but the two front ones, not having much wear
are hooped with leather instead. The distance between
the front wheels is 37in. and between the front axle
and hind one, 45in. A tall person would require a
little more-say 48in. In appearance, this form of
tricycle is very neat; being so narrow it partakes, in a
great measure, of that gracefulness of form so peculiar
to the bicycle. I am, bowever, bound to say that con-
siderable precision is required in its construction: the
back must be rigid, and the bearings, especially those
of the swivel and driving wheel, must fit well.
fore, I would not recommend anyone to commence
making a similar one, unless quite sure of good work-
manship. For those who are not practical mechanics,
but who nevertheless contrive to build their own
velocipedes, I would recommend a four-wheeler as
being easier to construct, and not requiring the same
rigidity or precision. With our Editor's permission,
I will be happy to forward a short description of a
light four-wheeler (571b.) which I have used for
nearly twelve months, and which has given me great
satisfaction, especially in regard to the ease of pro-
pulsion. The weight of the tricycle above described,
I may state, is 531b.

J. HASTINGS.

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When gas was first invented, or rather applied to domestic use, it was supplied direct from the retorts, rich, according to "C. D. C.," in condensable matters, and the consequence was, tar siphons had to be attached to each burner, and after many trials, the idea of using it in such a state had to be abandoned, and now, expensive purifying plant has to be provided and worked, all of which, according to "C. D. C.," might be disused and the gas supplied cheaper.

Then again, the use of benzole is not only to impregnate the gas with hydrocarbon vapour, but to lessen the heat, and the carbonic acid and sulphuric acid fumes, which he says are all supplied by the gas companies and charged as gas. If he can invent any apparatas for heightening the illuminating power, and at the same time purifying the material, I venture to say it would be no less a boon to the manufacturers than to the consumers.

Then as to his example, it proves the truth of what advanced in the commencement of this letter-that the fault of bad illuminating power is more with the consumers than with the companies. There is an Act of Parliament to compel the manufacturer to keep his commodity at a good and uniform standard, but there is none to compel consumers to adopt the best means of using the material supplied.

He starts by supposing" common gas" to be used in his experiment. I suppose he means that sent out of the works at about 14 candles, which is about the value ordinarily used. How is it that he only gets 2 candles out of it with his burner? He is grumbling at being supplied with an inferior article, and yet he goes the right way to work to make it worse still. If he really wants good results, why does he use a fish-tail burner, when they have been proved over and over again to be the worst kind possible for ordinary Newcastle gas? When his gas is carburetted by using 1 pint of naphtha per thousand-an item that will run up in large consumption-he only gets 7 candles, whereas, if he used an ordinarily good batwing, he would get about as much without any naphtha at all; and by using an Argand burner, he would, with a consumption of 4 to 5 cubic feet per hour, get a light equal to 13 or 14 candles, without any trouble; of course the loss in illuminating power would be in proportion to the distance he is from the works, and the state of the mains and services. I repeat, good burners are the only means of getting a really satisfactory result, either in power or cost; for he says, even with highly carburetted

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ment No. 1, p. 5, vol xi., with a very long connecting | gas, the difference can scarcely be detected by the
rod, compared with the length of the crank, would be
amply accurate enough for the purpose "Isometros" re-
quires it for. With a short connecting rod the figure
comes out perceptibly egg-ended, and my arrangement
is based on that same movement, only with what is
equivalent to an indefinitely long connecting rod.

J. K. P.

naked eye, and there would have to be reports, &c., made to the insurance companies; whereas with proper care with respect to burners and fittings, all this would be obviated, and without extra expense or attendance, and if people would only pay more attention to this seeming trifle, the companies would be less pestered and abused, and the consumer more contented.

LUCIDUS

[graphic]

NEW LATHE BY GEO. PLANT. [86] SIR,-You have published in your most valuable journal a print of one or two lathes by different makers, I therefore venture to enclose a photograph of one that has been recently built for me by Mr. George Plant, of Alsager. I trust the photograph will sufficiently explain itself, but as I am only, as in turning, an amateur, I will give you a few particulars. I have, of course, put as much as possible into the picture without any reference to the possibility of their being worked in combination, and this any turner will at

once see.

The lathe is a screw-cutting one, with the usual

NEW LATHE, BY GEO. PLANT.

change of wheels, the leading screw passing through the bed. The slide rest, when in gear, can then be either worked by the treadle, or if in spiral turning by the handle seen in front of the lathe. The head-stock has seven divisions, and the pointer or index is capable of being fixed in front, as shown, or at the back, which is often more convenient. The lathe has, of course, the usual micrometer screw arrangement, and the overhead motion,which latter has, by lever-sliding weights, a power of tightening or loosening the bands for driving the cutting frames. The photograph represents the geometric chuck on the mandrel, and the eccentric and elliptical on the bed. In the slide rest the elliptical cutting frame is placed. Beside these Mr. Plant has

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not only to our immediate ancestors, but which showed on to effect this purpose. Nor does the engineer
itself to the gaze of all when first the beams of the sun expect it to do so, for he knows that this must be
began to shine; for shadow is obvious to the view of all, obtained by minute calenlations on his part. If a
and, like its parent light, has been the occasion of man, "strictly speaking," must diffuse such know-
wonderful discoveries. When a ray of light is inter-ledge as Mr. Wood has been attempting, he must
cepted by an opaque body it is obstructed in its course, not only have a thorough knowledge of the indicator,
and shadow is the consequence. If it were intercepted but he must know the traverse of the valves, width
by a transparent substance it would be refracted with and depth of steam ports, and he must also know the
greater or less force, according to the density of the amount of modification the valves have. To illus-
substance; but where the body is opaque, it is not trate it we will take "Inquirer's" case. If his low
refracted, but obstructed, and the ray on each side of pressure engine valves have more modification on
the shadow still proceeds in a straight line, thus the edge than required (which seems somewhat
furnishing another proof that a ray of light passes manifest in the figure), he would have to put them
along in a straight line. Shadow affords the means of ex- forward unnecessarily to compensate for what they
plaining eclipses as well as of ascertaining the distance are veed too deep, thus inducing an unnecessary
of the sun from the earth. We can also tell by means of amount of lap on the high pressure valves. Just to
shadow not only the time of the day, but the altitude of illustrate that the modification of the valve edge
the sun, and consequently what sign of the zodiac he is would alter the amount of lap on the high pressure
shiming in, for as it was explained in a former letter he valves, we will suppose that the piston required in
gradually rises from a meridan altitude of 15 in our the vee aperture of the low pressure engine valves
latitude, until he has reached the meridan altitude of an area of 6in., to compensate for them being late,
62. When then his meridian altitude at London is 15, the vee to be 6in. x 2in. on the edge, which would
he has just entered Capricorn; add to this 234, his be an area of 6in., when the valve traversed from
greatest declination, and his meridian altitude will be bottom of vee to the top 2in., what the piston required.
384, at which height he will be in the equinoctial, add On the other hand, we will suppose the vec in valve
another 234, his greatest north declination, his meridan edge to be 4in. x 3in., which would give out the same
altitude will then be 62, when he has just entered amount of area as the first Gin.; but to effect this the
Cancer; thus his difference of altitude on each side of valves would have to traverse 3in., instead of 2in., so
the equator is equal to the extent of his declination. that the excentric would have to be put forward
Now it is obvious to every one that when his altitude is more in the latter case than in the former, thus in-
low the shadow of any object will be long, as Cowper ducing more lap to be put on the high pressure
speaking of his legs, says:
valves in the latter illustration than in the former.
Now, sir, I contend that Mr. Wood cannot, as he
said at the outset, tell how much ** Inquirer" must
put his excentric forward, except he knows the pre-
cise amount of this modification. As he can't tell
how much the excentric must be put forward, it is
useless for him to say how much lap he must put on
the high pressure valves.

Mine spindling into longitude immense, Provoke me to a smile: the shapeless pair As they, designed to mock me, at my side Walk step by step along the plastered wall, Preposterous sight, the legs without the man. The greater the altitude the less the shadow; and when the altitude is 45, or half way between the zenith and the horizon, the shadow is exactly equal in length to the height of the object which throws it. Thus, if a man 6ft. high cast a shadow 6ft. in length he might then know that the altitude of the sun or moon was 45.

Hence it is obvious that there is a proportion subsisting between the altitude of the sun and the shadow. That proportion is expressed by the following formula: Length of shadow height of gnomon:: R: tang. of the altitude. It is in consequence of this variation of the shadow that the ancients have divided the inhabitants of the earth into different names according to the shadows which they throw, as may be seen by the figure. The inhabitants of the torrid zone are called Ascii and Amphiscii-signifying without shadow, and shadows on both sides of them,-because when the sun is vertical, or exactly overhead, no shadow is thrown, which is at twelve o'clock in the day; and it is equally clear that the shadows of these people will be thrown both northwards and southwards, as for example, at the equator, when the sun is north of this line the shadows of those living there will be cast southwards; but when the sun has south declination, they will be thrown northwards. The higher any celestial object is, astronomers tell us, the greater

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the light and the more intense
the heat, so that the vertical

rays of the sun must dart with what is the cause.

great force upon the heads of

the inhabitants when no um

brageous tree affords its friendly branches to protect them. The inhabitants of the temperate zones have the name Heteroscii given to them, which is also derived from two Greek words, and signities those people who have their shadows opposite to one another at twelve o'clock in the day. Thus we living in the north temperate zone always see the sun in the south at twelve o'clock, and as the shadow is always in an opposite direction to the sun, we cast our shadows northwards, and our Heteroscii are those living in the south temperate zone, who, seeing the sun in their north at twelve o'clock, must east their shadows southwards; and of course the nearer we go towards the torrid zone, the shorter will our shadow become. Those who live in the frigid zones are called Periscii, because when the sun is above the horizon their shadows will go all round them. In the north frigid zone, for instance, at twelve o'clock in the day the shadows, like those in the north temperate zone, will be thrown northward, but as the earth revolves on its axis, its inhabifants will be carried to the other side of the north pole, and consequently at twelve o'clock at night their shadow will be east southward. This may be easily understood by the direction of the shadow in our latitude in the summer time, for the shadow of the gnomon on a horizontal sundial will go round a large part of the circle, and if the sun were above the horizon all night it would then go completely round the dial. The inhabitants of the frigid zone, then, will cast a shadow in all points of the compass in the course of twentyT. S. H.

four hours.

[88]

UNEQUAL STEAM PRESSURE. SIR,-As far as the use and practice of the indicator is concerned, I say that it will not tell the engineer everything about the steam engine as Mr. Wood pretends. For instance-a valve is 1-10th late, same as the figure Mr. Wood put in his last. The indicator did not say to him that he must move the excentric forward lin. to compensate for it; or if he went to an engine that had no lap on the valves, and he saw that it would do with as much lap on as would cut the steam off at half-stroke, the indicator never told him how much lap he must put

Now, sir, the original information which he gave to
"Inquirer" was too definite to admit the evasion
which he has attempted in his last, by saying that
it is an easy matter for any man who has a number
of engines under his care to loose the excentric, and
put it forward sufficient to make the low pressure
valves steam soon enough, and then take the high
pressure valve covers off, so that he could see what
amount of lap those valves required. This infor-
mation seems somewhat better than the original, but
he would not most probably give it in this form,
had it not been for what he considered my opposi
tion. Again, the information is as much at fault,
when given in this way, as the original. Though he
can see the amount of lap that would be required on
one side, when he turned the engine round to the
opposite side, he would find to his disappointment that
the other valve would either require more or less lap.
He has not told us what he would do in that case. I
expect he would do the same as many others I have
met with-i.e., put on unequal lap. Engineers of
practical experience believe in equal steaming, but to
effect this purpose they, unlike Mr. Wood, expect to
get equal steaming and equal motive power, when they
have equal aperture in valves, equal expansion, or cat
off, equal exhausts, and the exhausts to close up equal,
on both sides. If engineers don't get equal steaming
with this sort of valve setting, they at once inquire
If they find it to be induced by un-
equal balancing of the working materials they at once
set to and remove the cause, by putting sufficient
balance at some convenient and effective point in the
machinery. On the other hand, if they discover that
it is induced by the angularity of the beam or the un-
equal angling of the valve levers, they at once set them
right. But Mr. Wood adopts the earliest dodges almost
on record-i.c., of screwing this nut a bit and the other
a bit, a practice I am happy to know has passed long
ago into oblivion in the eyes of progressing engineers.
It is impossible to get a good figure in this way, or
equal steaming and equal strains in the machinery.
Again, if any brother reader requires information
through the medium of this paper on engineering, it
would be far better for those parties who require it,
and more credit to those who volunteer, to give it in as
direct a manner as possible, instead of the way
which I have just quoted. Again, he says in another
place of his last, when illustrating his case, that the
valves of No. 2 engine are in. late. Well, we will put
the excentric forward, so as to make these last valves
right. We shall then require in. of lap putting on the
short slides. Now, sir, it does not follow that because
both sets of valves are driven by one excentric that
they are of one traverse; but they evidently must be if
the low pressure valve; want putting forward in., and
then in. of lap putting on the high pressure valves to
compensate for it. What I said Inquirer "must do
was that he must put in. of lap on the exhaust side of
his valves (supposing that they steam from inside).
We will suppose that the valves are in. open on the
exhaust side when in the middle of their traverse.
Now let Inquirer" put in. on each side of the valves
on the exhaust side, then the valves will cover the
ports on the exhaust side in. Now let him shorten the
rods between fin., that will bring the exhaust of the
valves to the same point from whence they started, in.
open in the middle of their traverse. This done, he
has put in. of lap on the steam side of his valves, and
not the exhaust, as Mr. Wood has said. The reason
why I prefer lapping valves in this way is because very
frequently the steam sides of valves are veed or have an
uneven edge, which makes them more diffenlt to put
bits on; but the exhaust side of the valves being
always straight across the edge, or even, makes them
very easy to put bits on.
on nearly as soon as I could have the rods cut and
In fact, I have had bits put
pieced up again. But I don't look at time so much as

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I say, again, if "Inquirer" gets equal steaming with this amount of lap he will have no compression in his high pressure cylinder. (By equal steaming I mean equal valve apertures.) Mr. Wood's plan is that (as in the other case) the valves to be in. open in the middle of their traverse, to put in. of lap on the steam side by shortening the rods between lin. If the valve steam from inside that brings the valves on the exhaust side in. open, when in the middle of their tra verse. Yet he says the expansion is the same in both cases. Now, sir, as steam cannot be expanded in any cylinder with slide valves attached without making them longer on the face, it is evident that Mr. Wood completely stultifies himself. In cylinders that are steamed from inside by slide valves, expansion can only take place from the point where the steam is cut off to the point in the valve's traverse where the exhanst side of the valve comes in actual contact with the cylinder port, thus taking away the steam from the piston.

Just to illustrate this I will suppose that we have an engine whose traverse is in. and the ports 3in., the valve face to be just sufficient to cover the ports-i... no lap on either side. This arrangement would carry the steam on the piston the full length of the stroke pretty near at the same pressure as at the commencement. This is what we understand as no expansion. Well we will put 3in. of lap on these valves, not in the same way as an engineer, but in the same way as Mr. Wood advises ns-i. e., by shortening the rods between 6in., that would make the exhaust side of the valves wide open when in the middle of their traverse. A serious position that. This arrangement would cut the steam off at half-stroke with 9in. traverse; and as the valve-face had not been lengthened at the very identical spot where the steam was being ent off for the purpose of expanding it in the cylinder the valve would open on the exhaust side, and thus prevent expansion of steam from taking place. The valves, as well as exhausting sooner, return in their own traverse sooner, in the same proportion as he added less by shortening the rods between. Yet Mr. Wood tells us that the expansion is the same in both cases. The difference there would be in these two cases is that Mr. Wood's mode of lapping valves would be to strain the machinery without any profit the first part of the half-stroke; the last part, the engine would have to run without any motive power behind the piston to support its motion. In fact, the engine would be incapable of running if it had any work to do. He wants me to tell him how to lap valves without increasing the pressure at the commencement of the stroke. I have no idea that I can do that as a rule, except in engines that have no lap on the valves and the vacuum is very bad; but under such bad circumstances as these we may lap valves to a certain extent without increasing the pressure at the commencement of the stroke. Again when I lap valves (unlike Mr. Wood) I expect it to be a profit by reducing the terminal pressure in a greater ratio: hence the gain. Mr. Wood's practice is such that it strains the machinery when there is no chance of the terminal pressure being in any degree altered for the best. In No. 251 I find him giving "Relivot" information similar to that which he has been dealing out to "Inquirer." Without knowing anything about the pecul arities of the engine's construction, he says "Reli must put ĝin. of lap on the stearn-side of his valves; t in the next breath he says he must cut as much of the exhaust side of these valves. Now, sir, this would have the effect of straining the machinery without in aay degree altering the terminal pressure. For just as much sooner as he put the excentric forward, to com pensate for the lap, it would begin to exhaust. There is nothing gained by lapping valves in this way except unnecessary strains, as far as expansion of steam is concerned. Again, he talks about the practice and us of the indicator being a fine art. I say that the prac tice and use of the indicator is a science, not an art; hence science is knowledge. Art is the application of that knowledge to practical purposes. engineer succeeds so far with the use of the indica as to understand its delineation on the paper, then, not till then, will he be able to convert its teaching practical purposes. Now, sir, I contend that sud formation as Mr. Wood has been giving to "Inquir and "Relivot" cannot be diffused without knowing particulars of the engine's construction. Again. boasts of his superior knowledge of diagrams, and the many of your numerous readers who can speak his good judgment of the same. Well, we let parties speak when the spirit moves them in this direction. As far as my judgment goes the very figure which he gave to "Inquirer" and specified to be good, a progressive driver would scarcely consider worth his notice; and should think it would be much less so with a progres sive engineer. EDWARD MALBON.

PRE-ADAMITE MAN.

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[89] SIR,-Would it not have been better had J. Sargent, jun., enquired into the above subject somewhat more ere he challenged public discussion in the columns of your valuable journal-a journal, let me I have always found to be devoted to the notice of really useful and instructive subjects of general interest to its readers. Surely your correspondent cannot have of the Creation with the opinions enunciated by our read the "Book of Books," and compared the narrative best modern geologists and paleontologists, never have made such an application as he does in your last number now before me. Had he done so, in

or he would

stead of doubting the truth of the Biblical account, he must have been compelled to acknowledge the perfec

tion of the divine order of creation, inasmuch as man could not possibly have existed at the same period as those monsters shown in the fossil state at our British Museum, and by models in the grounds of the Crystal Palace, the earth not being then in a fit state for his reception.

Man being the crowning work of God, required that every subordinate thing should be previously perfection; and let sceptics sneer as they will, every new discovery only tends to re-verify the truth of the Mosaic description-leaving out all theory as to the duration of each day" mentioned therein.

Had man existed with the Ichthyosaurus and Plesiosaurus, &c., undoubtedly we should have found his bones as well as theirs, but such is not the case; and so far as I can learn, no instance has been noted of the discovery of human remains in any deposits except those of very recent times.

As one who signed the declaration of students of the natural sciences in connection with the scriptural account some four years since, I am not disposed to enter into any argument as to the truth or error of the latter, but I would certainly advise Mr. Sargent to look carefully at the subjects I have named and take-say Richardson's "Geology and Paleontology," published by Bohn, at about 5s., and make comparisons. If those do not convince him, I am afraid that no number of letters in the ENGLISH MECHANIC will do so. T. S. CONISBEE.

[90] SIR,-I see in the ENGLISH MECHANIC for 8th July that one of your correspondents wishes for a discussion of this matter. By "Pre-Adamite Man" I The use of the suppose he means pre-historic man. phrase "pre-adamite" is rather unfortunate. With Adam we have nothing to do, and we only raise a certain hulla-balloo if we speak of his predecessors. In our discussion of matters on natural science we have naught to do with what is called theology; that is a science to itself-having in it much that is true and much that is false. Adam may have been the first man or he may not. Science does not care to ask. All Science wants to know is, Whence did man come and when? The latter of these questions is the one your correspondent, I presume, wishes to raise. I suspect few will at this day restrict the period of man's existence upon the globe to the six thousand years until now prescribed to it. The numerous discoveries of flint flakes made within the past few years-the conclusions to which learned and thorough students of ethnology and geology have been forced to come-new truths learned from comparative philology and new insights gained into man's geological relations—these and other things have led most of our leading men of science to at any rate this conclusion, that the age of man as a species is not to be reckoned by thousands of years. Were it not that the opinion forces itself upon us that this subject is not the one best adapted for discussion in a journal designed for workmen rather than speculators, we might proceed to fill pages with a précis of what has been done in this department of science. Those who wish to make themselves thoroughly conversant with the subject can do so in the pages of Lyell, Page, and others. To those who only wish to know the general conclusion to which scientific men have come perhaps the following may be of use. I extract it from Page's "Man-Where? Whence? Whither ?" "Historically we can have no certain evidence of the outgoings and incomings of those early races which preceded all history. Even were tradition reliable and history certain, it is as impossible for the race as it is for the individual to trace itself back to its origin. We can only arrive at a notion of man's antiquity by inductive reasoning from the evolutions of nationalities, the growth of language and the progress of civilization; and the induction for all pre-historic time must be founded exclusively on the discoveries of geology. Geologically there is the amplest evidence of man having been an inhabitant of western Europe for ages preceding the popularly received chronology. Man's occupation of Europe does not fix the measure of his antiquity in northern Africa and Asia, to which everything points as the region from which the races of Europe were descended; and the discovery of pre-historic remains in Asia cannot be regarded as the earliest indications of the human race; but geology must seek for the earliest traces of man in the regions that are now occupied by the lowest varieties-thus implying an antiquity for the human species that cannot be expressed in years and centuries, but only relatively to other geological events." We may, I think, regard this as the conclusion which geology forces upon us-viz., that man has existed for ages, but that he is the last of the series of organized beings as he is the greatest. H. P., Hull.

I am

PEDESTRIAN TOURS. [91] SIR,-I have been a subscriber to your delightful and ever-improving periodical for nearly two years, and have derived much valuable assistance from it in my efforts as an amateur astronomer. glad to see the subject of pedestrian tours now engag. ing attention, and I write in the hope that I may be able to give, as well as receive, some information. For several years past I have spent my summer vacation in rambles through various parts of England and Wales, and can therefore speak practically as to the best mode of successfully carrying out such an expedition, and of the delight which may be derived from it. I have just returned from a week's ramble through Sussex, in which I have been solus, and during which I have visited many places, having walked upwards of 100 miles. In 1866 I took nearly the same route as that mentioned by your correspondent "B." in your last number, except that I started from Rhyl, and ex

tended my walk through Conway and Oswestry, as. far as Shiffnall. I have no doubt that many of your readers would like to undertake such a tour if they knew how to arrange it inexpensively. When I did the above-mentioned trip in company with a friend, we spent 11 days in walking, and I find from my diary kept during the tour that my If we share of the expenses came only to £2 1s. 8d. had adopted the plan suggested by "B," of breakfasting at a good hotel, our expenses would have been very much heavier. Our method was to sleep at an inn, to start on the first thing in the morning, and prepare all our meals out of doors with portable apparatus which we carried in our knapsacks. If any one wishes for information with regard to this apparatus, I shall be very glad to give it through your pages.

I want to get a hint or two, from any reader who has had experience in such tours, as to the best sort of boots or shoes for walking. I can walk any distance without becoming leg-tired, but with ordinary covering for the feet I get blistered feet, and this very much interferes with the enjoyment of such trips. In return, any information which I can furnish to intending tourists, either as to routes, places of interest, good and cheap houses for sleeping, or arrangements with regard to provisions, &c., will be most gladly given. Brighton, Sussex.

[92]

SCHOLASTICUS..

entire mass of the waters of the ocean for the first time on the surface of the globe, and providing a permanent medium of ultimate stability in the liberty of this mighty ocean pendulum. From this period meteorological changes took place, and the full developments of organized beings, by suitable climates, in almost infinite variety and in systematic order, adapted to the prepared conditions of the surface of the earth, were perpetuated by selection. LITTUS HABET CONCHAS.

SHIPS' PUMPS.

[94] SIR,-Permit me to thank "G. A. S." for his reply to my query, "The Goat and the Grassplot." I wish the above gentleman, or some one conversant with the subject, would inform me what he considers to be the best purchase for ships' pumps. The wee-gee and fly wheel are the best I know, and answer the purpose generally; but if a vessel spring a leak either will soon exhaust a crew, which I know from experience, having had to keep 22 hours at the latter purchase, after my crew were exhausted, in 1865. I have materially assisted the wee-gee by making a pendulum of a 121b. shot; but something much better than that is needed, leaving steam out of the question. CAPT. BAXTER.

35, Crane-grove-terrace, Holloway-road.

THANKS.

A CURIOUS SENTENCE. SIR,-The following is a curious sentence, and if you think it worth inserting, it will, I have [95] SIR,-I feel that I shall be doing no more no doubt, interest many of your readers. than to echo the sentiments of your optical readers by "Sator Arepo Teret Opera Rotas." returning sincere thanks to your talented correEnglish:-Cease from your work. The sower will spondent, the Rev. T. W. Webb, for his able exposition wear away his wheels! of the abstruse and difficult intricacies upon which optical definition depends. Such information from such an authority, and in a style so felicitous and unassuming, must, I am sure, elicit the warmest admiration of all, while it constitutes a painstaking and truthful analysis of principles which are generally too imperfectly understood, but are nevertheless of the highest optical importance. W. PURKISS.

1. It spells backwards and forwards the same. 2. The first letter of each word spells the first word. The second letter of each word spells the second word, and so on with the third, fourth, and fifth letters. 3. Beginning with the last word, the last letter of each word spells the first word, and so on with the fourth, third, second, and first letters.

Heads-buildings, Bridgnorth.

REG. PILKINGTON.

LUNAR COSMOLOGY.

[93] SIR,-A continued series of critical observations of the surface of the moon, by the aid of superior telescopes and repeated examinations, do not tend to establish the feeling that any corresponding physical resemblance upon the surface of the earth can be identified with the surface of the moon or suggest like causes of operation; but, on the contrary, in nearly every particular the surface of the moon is different to the surface of the earth, and also in the smaller gravity of the materials and the absence of meteorological influences in altering the surface during vast periods of time.

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THE OPTICAL BRICKLAYER'S TELESCOPE. [96] SIR,-I am afraid that "Optical Bricklayer may be a long time discovering the merits of his in. mirror, unless he adopts a more systematic method of proving its figure. Perhaps the valuable letters of Mr. Webb may help him to do this; if not, I would advise him to test it by the process described in the last volume of the MECHANIC, pages 332 and 357. This will set his mind at rest once and for ever as to the actual figure his mirror has.

The heavenly bodies are, perhaps, as a rule, about the most unsatisfying things which can be selected as tests of a powerful telescope, and while stars may no doubt render important service in the process of testing, on account of the almost infinite parallelism of Probably appropriate lunar names will ultimately be the rays which proceed from them, why they should used to distinguish remarkable and special appear- be considered test objects when focussed in the ordinary ances, and the words "seas" and "volcanoes" will disap-way, I am quite at a loss to know, and why it is that pear from the fanciful and poetic descriptions intended objects that are so exceedingly sensitive to atmospheric to represent popular resemblances to types on the earth. inequality as to be always changing, should be selected It is contended that the moon, as it at present exists, as standards of comparison is an enigma that I must is the union of what once were vast numbers of small leave to others to solve. spheres, with fluid interiors, of different sizes; that rings surrounded the earth like the rings round Saturn; that these rings were composed of an aggregation of small satellites; and that the whole identical mass of matter in a half fluid state has by the coalescence of the materials been united into one moon, and left traces of the multitude of small hollow spheres in the numerous craters and circular ridges, in the form of wrecks, which in some respects slightly resemble the craters of volcanoes, on the surface of the moon.

It is possible that the diameters of the small satellites varied from ten yards to 20,000 yards, and an ideal section of the moon in any direction would reveal the mechanical amalgamation of a variety of fractured spheres, and indicate the antecedent conformations. Perhaps any general inspection of the sectional interior of the moon would confirm the theory. The transformation of these flat rings, composed of an aggregation of small spheres or satellites, into one moon by an operation of gravity is one of the grand events of the past in lunar cosmology.

The vestiges left on the surface of the moon are chiefly the shattered remains of former small hollow globes, and these significantly indicate the relative proportion of thickness of the outer crust or shell and the relatively fluid matter in the centre of each small sphere. Probably the pleasure of tracing back some of the changes on the surface of the moon will appear as interesting as any intelligent investigation into natural history when contemplated as the work of immutable laws and the proof of design.

As a theory, the modus operandi will supply matter for discussion, such as the mineral characteristics of the interior fluid mass of each sphere, the distribution of the fluid masses over some parts of the surface of the moon constituting an appearance of flat planes, settlements, and floors, but still thickly filled in with the vestiges of former fragments of outer shell, and partially submerged in what was once relatively fluid mineral matter liberated by the fracture of the outer shells. In some directions, and radiating from a centre, these fluids give the appearance of the streams of lava from a volcano by the last distributions and settlements of the typical lava of the burst shells of the spheres or satellites.

At the same time that this great convulsion took place, an equally salutary provision was made upon the surface of the earth in the precipitation of the

It certainly seems feasible that a test in order to become so ought to be as exempt from change as any thing can be, and not be subject, as a star is, to endless distortions and caprices of the atmosphere. In this particular a thermometer bulb in sunshine has no doubt an advantage over a star, but a watch dial can scarcely be a test of definition with a large telescope, although it may be a moderately good test of achromatism in the case of a refractor; but, whatever test is used, the proper time for its observation (even with terrestrial tests) is of great importance. Noon is generally a very bad time. Perhaps the best time of all for steadiness is generally about one of two hours before sunset, especially after a cloudless day. "Optical Bricklayer" need not be at all surprised he cannot get on with Saturn. I may tell him, as an example of this, that two evenings since I was looking at Saturn with a 9in. reflector, and 3in. refractor simultaneously, and I got decidedly better definition with the 3in. than with the 9in., although the defining and separating power of the mirror is more than double that of the refractor. This simply shows how much atmosphere and aperture have to do with definition. As to stars, a power of 120 on a 74in. mirror, is scarcely enough at any time to give clear and sharp dises. Double that power would be far better if the mirror is truly figured; but, with every precaution, doubts may still arise, unless a mode of testing is used which does not depend on atmospheric conditions. W. PURKISS.

SECRET CODE FOR TELEGRAMS.

[97] SIR,-I purchased in London the other day a small work described as "A Secret Code for Telegrams, &c.," which I find has been extensively advertised and recommended. I think, however, that the author should acknowledge that hissystem is merely a rechauffe, with some very useless condiments, of one of the many methods given by Bishop Wilkins, in his "Mercurie, or the secret and swift messenger." The four imposing puzzle pages of alphabets at the end of this "Secret Code" made me at first believe that something new was concealed under them, but by using the worthy bishop's method I succeeded in producing the exact cypher of this modern writer, using his own sentences as examples. The method adopted by Wilkins is to write down, first the alphabet in its ordinary form, and

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EFGHI &c. Մ V W &c. If it were required to write the word babe the first letter would be N, which stands under B in the first line, the next I, which is under A in the second line; the third O, which corresponds to B in the third line, and

the fourth I from the fourth line. The next letter

necessary to use more than one plate. If the object has been already plated and part of the silver has worn off, the whole ought to be separated. The solution used for stripping off the silver is composed of strong sulphuric acid (vitriol) to which a little nitrate of potash is added; the article is laid in this solution, which will dissolve the silver, without materially affecting the copper, &c.; saltpetre is added by degrees, as occasion requires; and if the action is slow, a little heat is applied to the vessel which contains the stripping solution. The article should then be polished, cleaned

and treated as above.

in four parts of nitro-muriatic acid; water is then The solution for gilding is made by dissolving gold added, and the solution is treated with cyanide of pot. assium in the same way as silver. The solution should

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ANIMALS AS FELLOW BOARDERS. [101] SIR,-I beg to send you a few additional obser vations to Mr. Van Beneden's highly interesting paper on Commensalism," which was lately reprinted in Scientific Opinion:

would be taken from the fifth, and then the first, second, be heated when used. It is advisable to plate all animal which ought to be mentioned as an instance of &c., would be used again in order. Our " Babe," then Would be NIOI. The cypher words would be alwars articles before gilding. Three minutes will be quite lives in the "villages" of the prairie-dog. Aretorge

of the same length as the key-word, a space being left as the last alphabet is used. The difficulty of this cypher consists in the fact that the same letter has several different signs; thus B is first N, then O, whilst A and E are both represented by I. This cypher is described in full in the edition of Wilkins, published 1802, vol. ii, p. 39. It has only one objection, however, which is this, that if any particular word be certain of being found somewhere in the cypher, such as a proper name, or the title of a racehorse, &c., the whole can be unfolded in

I

a few minutes. If a few details of this method would amuse your readers I will willingly write again. have no wish to injure the sale of the little book, which is cheaper and more easily procurable than Wilkins's, and contains also an ingenious notion as to numerals, which I have no right to publish. I do not doubt his good faith, and can fancy his exclaiming Pereant, qui mea ante me dixerint,

or, in the vernacular,

Confound the nasty scribes, and those who tanght them, Who thought my thoughts before I ever thought them! CRYPTOGRAPHER.

ELECTRO-PLATING AND GILDING.

sufficient to gild any article.

with gold, or when the gilding is imperfect, and the Before regilding articles which are partly covered articles require regilding, the gold should be removed from them by putting them into strong uitric acid, and when the articles have been placed in the acid, by adding some common salt, not in solution, but in Crystals. The articles should then be polished and treated in the usual method.

Thus far, Mr. Editor, I have endeavoured to answer M. Schneider, and shall be willing to reply to any further queries that I am able. 258, Kingsland-road.

CDE

WALTER J. NICHOLLS,

SQUARING THE CIRCLE.

[99] SIR,-Seeing that one of your abler correspondents in last issue of the ENGLISH MECHANIC has tried so impossible a task as that of squaring the circle-I mean the rectifying of the circumference of the same figure-you will no doubt allow me to give to those interested in the subject a more precise and perhaps through the medium

more valuable construction of your

columns.

I refer myself to figure annexed, so as not to encroach too much on the space offered to your sub

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[98] SIR,-I think M. Schneider [4228] will find the following a most efficacious method to pursue for electro-plating and gilding. The solution of silver used for plating consists of cyanide of silver dissolved in cyanide of potassium, which may be prepared in various ways. The method generally adopted is as follows:-Metallic silver is dissolved in four parts of nitric acid, diluted with one part of water; the diluted acid is heated in a vessel, and the silver is added by degrees. M. Schneider must avoid breathing the fumes which ascend, as they are highly deleterious. The metal being dissolved, the solution is emptied into a larger vessel and diluted with water. To this is added a solution of cyanide of potassium, so long as a precipitate is formed. This is cyanide of silver. When the precipitate has settled, the liquid is decanted, and the precipitated cyanide of silver is thoroughly washed A G is a perpendicular to the said diameter, and F a so as to effectually dissolve out the soluble salts. A point on the same, fixed so that A Fr, and A G may solution of cyanide of potassium is then added to the equal the linear distance F C. F has been joined with precipitate until it is all dissolved. The resulting E, and through G a parallel to FE (GH) has been liquid constitutes the cyanide of potassium and silver, drawn, intersecting the prolongation of the said diaand forms the plating solution. It ought to be filtered meter in H. AH represents exactly up to the 5th deciprevious to using, as there is nearly always formed a mal incl. the rectilinear length of the circumference, black sediment composed of iron, silver, and cyanogen, for by similar triangles A F C and A G H, we have which, if left in the solution, would fall upon the surface AF: AG AC: AH, of the article receiving the deposit and make it rough. The cyanide of potassium used to dissolve the cyanide of silver may be so diluted that the plating solution, when formed, shall contain loz. of silver in the gallon. Articles that are to be plated are first boiled in alkaline ley, to free them from grease, then washed from the ley, and dipped in dilute nitric acid, which removes any oxide which might be formed upon the surface; they are afterwards brushed over with a hard brush and very fine pumice (known by oilmen as FFFF). or AH= The alkaline ley should be in a caustic state, which is easily effected by boiling the carbonate with slaked lime, until, on the addition of a little acid to a small drop of the solution, no effervescence occurs. When the lime has settled, the clear liquid is fit for use. The ley should have about lb. of soda ash, or pearl ash to the gallon of water. The article being thoroughly cleaned and dried, has a copper wire attached to it. It is then dipped in nitric acid as quickly as possible, and washed through water, and then immersed in the silver solution and attached to the battery, as at A in Fig. 1. In large manufactories, where a great many FIC.2 8

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Is not the burrowing owl (Pholeoptynz hypogāra) un commensali. m? In the prairies of the far West i ludovicianus). It is reported that even rattlesnakes are abundant in these villages," and that the quadharmonious juxtaposition. ruped, the bird, and the reptile may often be seen in In the pampas of South America a closely allied species (P. cunicularia) associates with another burrowing rodent, the vizcachs

II., 12; Brehm, "Illustrirtes Thierleben," III., 601, agostomus trichodactylus). (P. L. Sclater, in Nature, 602; Azara, Apuntam, I., 214).

Max.) (Culebra de dos cabezas," or two-headed snake) I have repeatedly found Amphisbæna flavescens (Pr. in the nests of a species of ants called in this country "bachaco" (Atta cephalotes, L.). The Amphisbæna feeds on ants, as is clearly proved by the contents of its stomach. It is, however, more than probable that the reptile and the insect are not in an exclusively hostile relation. The bachaco" is a remarkably strong and audacious insect, a giant of the myrmidonian tribe, and the number of inmates in one nest being very large, it would no doubt be an easy matter for them either to drive out or to kill the sluggish intruder. Richard Schomburgk ("Travels in British Guiana," I., 240), mentions a similar association between Atta cephalotes and another reptile, which he calls Cecilia annulata. (Is this Cæcilia lumbricoides, Dand., or Siphonops annulata, Spix. ?)

A great many insects are found in ants' nests, amongst them many bettles, either only during their larval condition, as, for instance, the rose chafer (Cetonia aurata), or during their whole life, as many brachelytra (Myrmedonia homechusa), Claviger foveolatus, Dinandra Maerkelii, &c. The last two beetles are perhaps no true fellow-boarders in the colonies of the ants, but a kind of "domesticated" animals, reared and kept by the ants on account of certain substances which serve as food to their hosts.

A case of true commensalism among mollusca came not long ago to my notice. A small bivalve sheil, Sphærium modioliforme, Anton (which, I may add en passant, is the only fresh water bivalve I have hitherto found near Caracas), lodges in the deep umbilical cavity of the shell of an Ampullaria, It is the form called by Philipps A. crocostoma, which however appears to be identical with the old A. ejusa, Chemn. This shell is exceedingly common in our rivulets and ponds, but though I have examined hundreds of specimens, I have found not over two dozen of shells of Spharium. It is certainly convenient for so small an animal as this bivalve is to attach itself to a larger species, provided with more developed means of locomotion. Caracas, June 16, 1870. A. ERNST.

THE AMALGAMATION MOVEMENT. [102] SIR,-Although hitherto I have been but a silent reader (and that merely cursorily) of your contemporary, the British and Foreign Mechanic, I cannot allow the present opportunity to pass without congra tulating you, and in particular the readers of that 146 journal, on its approaching amalgamation with "our" MECHANIC, in whose extended sphere of usefulness I am confident they will find what has hitherto been wanting in their own periodical. The MECHANIC is no longer the "rough casting" it came to its present editor's hands, but is now the finished article that superior skill and refinement alone could make it. After endeavouring in vain to enlighten the universe, your contemporary must feel indeed highly honoured by being merged in the blaze of the ENGLISH MECHANIC. I for one congratulate it on the honour it has achieved, and the pleasure it must feel in joining the goodly company of Scientific Opinion and The Mech in the world-encircling arms of our Alma Mater-the ENGLISH MECHANIC. The readers of the British and Foreign while, perhaps, regretting that sic transit gloria to-day," may with renewed vigour exclaim, To-morrow to fresh woods and pastures new!"

which result shows a difference in the first seven decimal places, when compared with the Ludolphine () of seven units in the seventh decimal, and not already in the second, as in Mr. Proctor's solution.

A MEMBER OF THE ENGLISH MECHANICS' SCIEN TIFIC AND MECHANICAL SOCIETY.

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things are plated, a Bunsen's battery is used, but fo amateurs a Daniel's would be best. The article is instantaneously coated with silver, and ought to be taken out, brushed, and replaced. In the course of a few hours it is taken out again, brushed and polished. Fig. 2 will illustrate the plan pursued in large establishments. D is a large vat containing solution; B and C are two brass rods placed along the top of theirs. I tried it again, and again still the same the vat and to each of which a wire from the battery results. I then computed it by "Mercator's" is attached. The advantage in this arrangement is principle-(i.e., supposing the earth to be a plain), that you can have more than one rod across the vat and found it to be 5,729 miles, which comes nearer from each pole as a, a', b. This plan is generally adopted to Mr. Dyer's distance, but it should be rememwhen there are a great many articles and it becomes bered that angle J is much too small to give this

SOUTH

POLE

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[103] SIR,-It is said that the British and Foreign Mechanic, after a troubled existence of nine or ten months, is about to terminate its not very glorious career by permitting itself to be merged in "ours." Well, I am not surprised at it; in fact, from what I have heard for some time past, I expected it would have "paled its ineffectual fires before this. Better late than never. Though the individual dies the nation lives; and though scientific journals perish individually, the ENGLISH MECHANIC, by some means or other, absorbs the best portions of their animating spirit. Who would have thought that your paper, with its unassuming title, would have grown so rapidly, and attracted to itself by virtue of its central power so many of the lesser intellectual luminaries? You have, Sir, achieved a great success; you have, as Mr. Proctor says, "an enormous circulation," and you are exerting, no doubt, a salutary influence over large numbers

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