The remainder of the meeting was taken up in discussing the above-mentioned subjects, and in bringing forward questions relative to pistons, guidoscopes, and pedometers.

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, 31, Tavistockstreet, Covent Garden, W.C.

able to J. PASSMORE EDWARDS.

will rise and fall with a westerly deflection, rebound
through a like path, and so hop westwards round the
earth. On the other hand, if a ball be dropped from
a fixed point above the earth's equator it will fall east-
wards, rebound with eastwardly deflection, and so hop
eastwards round the earth-to meet the other, belike.
The case is, however, not unlike the cup in a pie-dish
32ft. high, or the problem of the elephant and the fly,
where the weight of the elephant might be neglected,
or (to conclude), Watson's famous problem of the man
with a perfectly spherical head surmounted by an
infinitely high conical cap.
RICHD. A. PROCTOR.

I

THE SATELLITES OF URANUS. [357] SIR,-In reply to "Etudiant" (335, p. 591), I should be very glad to look up the papers he refers All Cheques and Post Office Orders to be made pay- to; but, as I mentioned to you some time since, I am quite overpressed with work of one sort and another just now. Let me remark, however, that as his notes show that the epoch 1851-2 really was in question, have no doubt that the simple difficulty of determining the place of maximum elongation led to the seemingly contradictory result. I made the ellipse have axes as 7 to 10 by a geometrical construction; but taking 6 to 8 "Etudiant" will see that in such an ellipse, if lines be drawn from the centre, inclined 10 or 12 degrees to the major axis, their length will differ very little indeed from that of the half-major axis. Considering the difficulty of measuring the distance of a sasellite of Uranus from its primary with extreme accuracy (even when so powerful a telescope as Mr. Lassell's was used) it may safely be held that no attempt to determine the position of the apparent major axes of the satellites' orbits could be satisfactory.

"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 does, 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.

In order to facilitate reference, correspondents when speaking of any Letter previously inserted will oblige by mentioning the number of the Letter, as well as the page on which it appears.

RICHARD A. PROCTOR.

LUNAR COSMOLOGY.

[358] SIR,-Will "L. H. C." (218, August 26, p. 545), kindly favour your readers, including your humble servant, with the titles of those works which constitution of objects on the moon's surface, as well as contain reliable information relative to the chemical the basis of his own conclusions thereon? We shall all be much interested in learning the chemical, or at least mineralogical character of the central mountain of "Aristarchus," which Professor Phillips compares with white trachyte, also the nature of the dark floor of "Grimaldi." Assuming that "L. H. C." are the initials of "Littus Habet Conchas," and that the "continued by the aid of

and what can we say to those persons (f the g
such) who give testimonials that this utter
is effected by the patent apparatus of Mr. A
such testimonials possess no more valor &
no more of the element of truth than wa
testified that perpetual motion had been &,
was to be seen at work every day at Bra
what can we say to Mr. S. Crompton du
in the number for July 8th assures me.
figures may say to the contrary, that the ve.
per cent.' saved in fuel, is not a delusio
fact with feed-water heated to 212-." 1.7
Crompton, by careful and trustwort
proved the truth of these statements big de
coal used, week for week doing, the f
work with the engine in both experime
say, one week with the cold water, the a
the water heated to 212 with the • econ.IY)
cases the statements have been fully coLETZEL
I say to Mr. Crompton is simply this,
bungled the matter somehow, and has sBETE
ceiving himself. It is more charitable to an
to say he is trying to deceive others, beers
donbt he either has done the one, or is tre
the other.

To show the unreliable nature of Mr. C

statements and experiments, I shall cau
count of another impossibility which he reish
stantially of his "economiser."

14-horse engine he heats 6,000 gallons of water in
He says that with the waste steam from à Ja
to 212. Now what amount of heat is containe
waste steam escaping from a 14-borse engine r i —
and what amount of heat is required to race h
gallons of water to 212 from 40 7
If up to
tion we find the latter quantity to be a great deal
than the former, I suppose we shall be justified is-
ing that Mr. Crompton is a gentleman shu d
ments should be received with great can

A gallon of water at the average temperature e d is to be raised to 212", it must therefore have 172 udé d to it.

1,200 of heat in it, and in warming to 21
A gallon of water in the state of 5% sing ber
parts with 988 before it falls to 219 them are are
sufficient to raise 574 gallons from a 2 1st #f
we divide 988 by 172-the differes bevern 40 and
212-we get 574 for a quotient) as a wat 54
gallons of water at 40 can be raised to lis

densation of the steam generated from one games of sour
will be 674 gallons of water at 212.
under a pressure of 55lb. per square inch, and the pa
This is the thes
retical maximum, which in practice is never reached a
long chalk."

The fact is, "T. A.'s" reasoning never seemed to me to render a defence of accepted theories necessary at all. He seemed to be in the dark as respects light. "T. A." will get hopelessly fogged, I fear, if he attacks the question whether "the powers and activities of material substances result from the action of properties they inherently possess" or not. There is a stated in the last letter, his own, not yet given to the hour for steam, bnt Mr. Crompton says his emite es

volume to be written on every noun, adjective, verb, and adverb of that portentous sentence; and I would not have him be too confident that he will find a prevailing belief to fight with.

RICHD. A. PROCTOR.

superior telescopes and repeated examinations," are, as

selenographer able to compare them with others, and
public, would it not be desirable to forward copies to a
to examine them, not in connection with any given
theory, but for the purpose of noting points of simi-
larity and difference? I quite agree with "L. H. C."
in the importance of "accumulating additional obser-
vations;" for assuredly our knowledge of the moon's
surface is very limited, and the study of "Selenology,"
employing this term as the lunar analogue of
"Geology," has as yet scarcely commenced. While,
however, observations are scattered here and there,
some published, others unpublished, each observer
being prone to form and adhere to his own theory, but
little progress can be made. Selenography, more than
any other branch of astronomy, stands in need of co-
operation. We may pick up many shells on the sea-
shore, and replenish our little cabinets; but it is the
experienced naturalist who alone is capable of so
studying them as to advance biological science.

[359]

W. R. BIRT.

DELUSIONS CONCERNING THEM.

SIR,--The total heat of steam whose pressure is 401b. per square inch above the atmosphere, or 55lb. total pressure, is 1,200 degrees, counting from zero. The average temperature of river water the year round in these countries is, I believe, 40°; therefore, if a steam boiler be supplied with water at 40, and it is to be raised into steam of 55 lb. total pressure, it must receive 1,160 of heat from the fuel in the furnace; 25 per cent. or one fourth of 1,160 is 290, and any feed waterheater which professes to save 25 per cent. of the fuel used in generating 55lb. of steam from water at 40, must send the water into the boiler at 290, and no less. But that is impossible, and to profess to do it is false and absurd.

A nominal 11-horse non-condensing engin", erk without expansion, requires 14 cubic feet of water pr

than 8 cubic feet per hour-for steam when cut of
half stroke has its efficiency increased from 1 to 1
But in order to show my generosity to Mr. Crompie
which my great advantage over him enables me
without feeling it, I will say his engine uses 12 e
feet of feed-water per hour or 75 gallons, or 750 galice
per day of ten hours, and that is the quantity of w
in the state of steam which passes into the cylinder
capable of raising 574 gallons from 40 to 212.
that time; and as each gallon by its condensation
of 6,000, as Mr. Crompton asserts.
arrive at a total of 4,305 gallons heated to 212 inste
But upon loose.
a little closer into the matter I find that a con-ideras
deduction must be made from this 4,305 gallons,
to, for all the heat which leaves the boiler on its was
else from the temperature it is presumed to be ra
the cylinder does not pass into the water-heater. 2
one-fifth of it at least is converted into work in t
cylinder and disappears altogether, and not less tha
one-twentieth is dissipated by the exposed surfaces it
fourths of the heat which leaves the boiler on ile may
to the cylinder ever reaches the water-bar
and the 4,805 gallons as found above must be re
to three-fourths of itself, or 3,229 gallons, to w
must add the 750 gallons resulting from the codes
steam, making altogether 3,979 gallons, and ta
greatest quantity of water which it is possib
from 40 to 212 in ten hours by the waste st
a 14-horse engine, and even that requires
particle of the steam should be condensed in the w
that not a breath of it escape from the waste a pie
(pipe G in Mr. Crompton's drawing), but the d
is impossible of fulfilment, for as long as pipe is there
a considerable quantity of steam will always ee
from it.

off at half stroke, therefore it should not require

CURIOUS QUESTION. [356] SIR,-I had not noticed Mr. Usborne's enery at p. 450 (as addressed to me), and now referred to in letter 844,p. 593, or I should certainly not have “ignored it altogether." I have, therefore, so far as his question ON FEED-WATER HEATERS, AND POPULAR the cylinder and pipes, &c., thus no more than te is concerned, no views to revise; my silence implying no opinion either way. But as in reply to a left by "M. L." (236), p. 518, I had indirectly dealt wit the question, and had (I find) made a mistake, I take the opportunity of now admitting as much. In my rapers on "The Earth: her Figure, Motions, &c.." I had enunciated the first principles on which the problem is to be dealt with; but in reply to "M. L." I applied these principles somewhat too hastily, and so came to an erroneous result. My mental reasoning was somewhat on this wise: a ball let fall from a great height has a slight easterly deflection, while a ball fired vertically upwards has a slight westerly deflection while rising; the westerly deflection during the rise of such a ball will be counteracted by the easterly deflection during thall, and there will therefore be no deflection at all whethe ball has reached the ground. The same reasoning applies when the ball is fired at an angle with the verticalhence the easterly and westerly range of balls fire at equal angles to the horizon, and with equal velocities, will be equal. But the reasoning is wrong, and does not apply to either case. The ball will have westerly deflection from the moment it leaves the ground el to the moment it returns to that level; for in falling its condition is not that of a ball let fall from a úxed support, since at the moment it begins to fall it is actually travelling westwards.

I have not followed the correspondence on this matter so cannot tell what " F.R.A.S." may have said. If, answering Mr. Usborne's question directly, he has said that there is no deflection, it has doubtless been through the same inadvertence that led me wrong.

Here, by the way, is an old result of the "enrions question," and the principles it depends on. If we conceive a perfectly elastic ball to be fired upwards from the earth's equator-the earth being conceived for the nonce to be a perfectly smooth sphere-the ball

Water cannot be made hotter in an open vessel (that is to say, one which is in free communication with the atmosphere, whether covered or open) than 212, but 212 is only 184 per cent. of 1,160. It appears, therefore, beyond the possibility of doubt or dispute, that 18 per cent. is the greatest saving which it is possible to effect by warming the feed water by the waste steam, and that is the greatest theoretical saving which we can show even upon paper; but that is not, never was, and never will be, effected in practice, for even if the water is got up to 212 in the "heater," it will lose several degrees on its way to the boiler through the pump and pipes, and from this cause alone the practical effect will always fall below the theoretical promise.

This is rather less than two-thirds only of what Mr. Crompton says the heater is doing. He mot therefore be mistaken in either of three ways. the engine must be a great deal more powerfal (50-p at least), and use a great deal more steam that be supposes, or the quantity of water passing through the heater must be very much less, or at a much lower temperature than he asserts.

25,

Suppose his assertion is true that 6,000 gallons é really pass through the heater per day, then the tem perature of that water can be no higher than 170 stead of 212), and as Mr. Crompton feeds his bos with this water, the saving of fuel by doing so is only 11 per cent., or not one-half of the inevitable" for which he so persistently sticks up, and this I ad What then are we to say to those persons who per- fully convinced, from my own observation and experi sistently assert that their feed-water heaters save 25 perence of feed-water heaters, is as much as nine ont of cent. of fuel? What can we say but that these state- every ten of them are doing in the ordinary way of ments originate either in utter ignorance of the natural laws which govern that operation, or else are put forth for the purpose of misleading the public and obtaining orders for their wares by hook or by crook ;"

rbe so easily obtained for the purpose, and a saving even 10 or 11 per cent. is not to be despised; but let man expect much more, for if he does, he will surely disappointed.

have no hesitation in saying that Barton's heater s good as any that can be adopted. I like the cut it on paper very much, though I never had the asure of seeing it in operation, and I feel quite sure t it is capable of doing as much as it is possible to in the direction of saving fuel by warming the d-water, and I also freely admit I consider the ign of it greatly superior to many others that I re seen and which bore a very good character as Economisers," but such wild, unfounded, and untenle statements as Mr. Crompton has made respecting are only calenlated to throw doubt and ridicule on it, and to bring a very excellent article into disyute, and Mr. Barton might well cry out, "Save me m my friends." JAMES BASKERVILLE, Manager, City Foundry, Limerick.

SCREW POWER.

1360] SIR,-In my letter on the above subject, on 592, your dranghtsinan has made my screws leftinded, instead of right-handed, which matters not in Fig. 3, but has made a mess of Fig. 1.

SPECULUM WORKING.

J. K. P.

combined.

surface that will bear washing after the deposit is effected. I have manipulated principally with the tartrate of soda process, requiring heat and sunlight I have tried this process, with and without sunlight, with and without heat, and with weak and strong solutions. Lastly, I tried Browning's formula, as given in his "Plea for Reflectors," and allowed the speculum to rest in the solution 8 hours. The result, to my surprise, was a bright deposit of silver, only a portion of the surface being slightly clouded with a bluish film, which I thought would instantly disappear on the application of a little rouge. I was extremely careful in washing the silvered surface, pouring the water on from a cup-yet a portion of the surface was torn. I used hard water in washing, as I did on the other occasions, and distilled water for the solutions. The water was of the same temperature as the speculum. After I had been pouring for a few minutes a portion of the silver surface began to assume a dull appearance. On close examination this proved to be clusters of small blisters. (I should be glad to hear the explanation of this phenomenon.) Though the blisters flattened as drying took place, they left their outlines: but, on the whole, there is a capital polish, though I have administered no rubbing whatever; indeed, to do so would be to rub the silver off altogether. I want a surface that will bear polishing when tarnished, and should be rejoiced to hear of a certain process, or of Mr. Purkiss's method of procedure. I cleaned the speculum before immers. ing in the silvering solution with whiting, then with strong nitric acid, washed well with common water, then with distilled water, and finally with alcohol, and immersed the speculum wet with the alcohel. I have frequently obtained a deposit that would adhere well in patches, and in one instance at least, towards the edge. of the speculum, I obtained a ring about 4th of an inch wide, that I could not rub off with my fingers, even I am quite unable to account for this. scarcely be expected that all operations will go accomplish with my speculum, supposing it to be a I should like to know what I ought to be able to smoothly in a first attempt of such a delicate matter as speculum working, however lucid the instructions may good one; it is 11 in. in diameter, and 18ft. focus. be; something or other will turn up unexpectedly for Will Mr. Purkiss be kind enough to tell me? I wish which instructions make no provision; then it is that to test with terrestrial objects, that method being most we find our MECHANIC SO invaluable. It is surprising convenient to me at present. I can command space of as well as pleasant, even to those not immediately in-buildings, a turret clock, or human beings. I did not about a mile, and at that distance the objects may be terested, to see how readily and disinterestedly information is given in "our" pages. construct the testing rod described by Mr. Parkiss for Having failed in polishing my speculum I began ascertaining the figure of the speculum, or I might again, as Mr. Parkiss advised me to do, but not before perhaps have known what figure I had obtained with I had laid the glass aside for some months, partly to little trouble. I have never had the pleasure of lookattend to other matters, and partly to allow breathing ing through a good telescope of large diameter, but as time to brace up for the renewed effort and the troublefar as I can judge I have reason to be satisfied with consequent thereon. I rough-ground the glass for mine. I by no means regret the trouble I have bestowed a few hours, then commenced testing the iron tool to on it. I can use the whole diameter of the speculum, make it coincile with the curvature of the glass, which even with what I believe to be a high power, on tercarve I took for granted was spherical. This testing the Herschelian form (aerial). Mr. Purkiss questioned restrial objects. I have temporarily mounted it in is really a tedious process. I was about sixty hours in accomplishing this to my satisfaction. I renewed the the advisability of my making a speculum of such a oil and lampblack on the speculum several times, and long focus; but I may mention that I can adopt an spoiled several files; indeed, it was with great difficulty arrangement of my own, possibly akin to the pancratic I could get the files to bite at all after a few minutes eyepiece, whereby I can use the speculum at any length work. I verily believe they supplied me with a disc of within the focus, and which is convenient for terrestrial steel at the foundry instead of iron. If Mr. Purkiss purposes. May I not expect good results in viewing will inform me if he finds a similar difficulty in filing planets by using a cap next the eye with a very small the oiled iron, and if the time I have stated would be considered by him much too long for the operation, I should be obliged.

[861] SIR,-Allow me to sincerely thank Mr. Purkiss for so kindly coming to my assistance when I as in trouble with my 113in. speculum, and for his aluable series of articles on speculum working. Those articles no doubt, thoroughly practical as they are, have induced many to undertake the working of a speculum for themselves; they had the effect of stimnlating me to renewed efforts after I had failed. It can

when wet.

hole in it?

As it is my intention to work another speculum of the same diameter and focus, I must plead this as my reason favour me by explaining my seeming misadventures, for detailing my experience, hoping that Mr. Purkiss will needful, as he seems so well able to do. Perhaps I am and giving a hint or two on those points he may think the only one of "our" speculum workers who has met nothing about them. Are there any who have begun with difficulties in his labours, as we hear little or

Lockyer's first lecture, delivered on the 6th of December,
1869, and published in the Journal of the Society of Arts
of January 14th, 1870, page 153, it is stated, "Newton
made a round hole in a shutter for his experiments;
but we now know he ought not to have done that; he
But this did not come out
ought to have made a slit,
till 1812 (1802 ?) when Dr. Wollaston, by merely using
a slit instead of a round hole, made a tremendous step
in advance." Other statements of the same import
were frequently made by Mr. Lockyer in his course of
lectures.

Are these statements of Prof. Roscoe and Mr. Lockyer conformable to facts? Did Newton in his experiments confine himself to a round hole as alleged by these savants? The statements not only are not conformable to facts, but are directly opposed to facts. We have the refutation of them in Newton's own words, by which it plainly appears that he used in his experiments not only a round hole, but "an oblong slit 1-20th of an inch wide," and also a triangular hole. In Newton's "Optics" (edition of 1704), page 49, it is stated "Yet instead of the circular hole, 'tis better to substitute an oblong hole, shaped like a parallelogram, with its length parallel to the prism. For if this hole be lin. or 2in. long, and but a 1-10th or 1-20th of an inch broad or narrower, the length of the image (spectrum) will be as simple as before, or simpler, and the image will be much broader, and therefore more fit to have experiments tried in its light than before." Hence we find that Newton used the very width of slit which Prof. Roscoe and Mr. Lockyer assert he did not And, further, they allege that if he had used the narrow slit, he would have discovered the spectral lines. He did, however, use the narrow slit, but did not discover the spectral lines.

use.

Lockyer had read Newton's "Optics," they would It is quite evident that if Prof. Roscoe and Mr. scarcely have ventured to make such palpably

erroneous statements. Indeed, if they had even read
Light, Vision, and Colour," and the "Treatise on
more recent works on optics, such as "Priestley on
Optics" published by the Society for the Diffusion of
Useful Knowledge, they would have found that Newton,
in his optical experiments, used the narrow slit, which
they allege he did not use.

several very erroneous and inaccurate statements are
Throughout the whole of Mr. Lockyer's first lecture,
made. For instance, in the Journal of the Society of
Arts, for January 14th, 1870, page 155, he states, "You
see, therefore, that our spectroscope depends first of all
on Newton's discovery of the prism in 1675." Mr.
Lockyer ought to know better. He might have known
that the prism had been used in optical experiments
by the Italian philosopher, Grimaldi, long before the
time of Newton's optical experiments. This is evident
from Newton's "Treatise on Optics (edition 1704,
referred to by Newton himself.
page 23), where Grimaldi's experiments are specifically
Hence the prism was
not discovered by Newton as alleged by Mr. Lockyer.
Dr. Priestley states in "Light, Vision, and Colour,”
that Grimaldi perceived that when a beam of the sun's
light was transmitted through a prism, instead of
coming out round as it entered, it made a very con-
siderable oblong image (spectrum) of the sun on the
opposite wall, by which he proved that colours are pro-
duced by the refraction of light without any reflection;
and, further, that Grimaldi's" Treatise on Optics,"
giving a detailed account of his experiments, was pub-
ments.
lished before Newton commenced his optical experi-
E. NUGENT.

MR. DAVIS'S ARTICLES ON CHEMISTRY.
[363] SIR,-Will you allow me in all kindness to

When I had tested the iron tool so far that every square on it was marked by the oiled glass, I commenced the fine grinding on the polishing machine described by "Arcturus" some time ago. (Mr. Purkiss, of course, recollects the construction of this machine. There is no side motion to it, and I should be glad to know if Mr. Purkiss considers the side motion and have given up in disgust-banished the subject offer a suggestion to Mr. Geo. E. Davis, the writer of to be indispensable.) Having completed the fine grinding, and this I considerably prolonged, I pro- is to be accomplished, even by inexperience, assisted from their minds for ever? Let us hope not; something ceeded to construct the pitch polisher. I had a die made as recommended by Mr. Parkiss, which would by "our" kind contributors, and our own energy, as impress eleven grooves each way on the pitch. But in my 11 in. mirror proves.

SPECTRUM ANALYSIS.

J. P.

the chapters on "Chemistry," in the MECHANIC? I am afraid he has mistaken the class of readers for whom he is writing. He promised at the outset that the chapters should be of a thoroughly practical nature, and at once he plunges into theory. Under the head of "Atomic Weights," why not have given the method of finding them from the specific heats of the metals referred to-lithium as unity,--and the real method of

impressing the grooves I obtained an impression of the air-holes in addition. This appeared to be unavoidable. However, I cut off the projections as neatly as I was able, and passed on to the moulding of the pitch to the mirror, which after some trouble I accomplished, warming the SIR ISAAC NEWTON, PROF. ROSCOE, MR. NORMAN finding the exceptions, such as carbon. Instead of say

pitch by the heat from a fire. By the time this was done Some of the grooves were almost invisible. I then widened the grooves with a chisel (and I will here whisper to Mr. Purkiss that I chopped off several of the facets). The next operation was polishing. This was now a moment of anxiety. I applied the rouge, and in one minute I obtained what I failed to obtain on a previous occasion in 120 hours-a polish. But the polish could only be observed round the edge. The Speculum worked somewhat stiffly, but I continned until it began to revolve the reverse way to that of the tool. I thought there was something wrong then, and, remoulded the pitch and cut the facets smaller, hoping thereby to rectify this defect. But I could not do it. The speculum persisted in revolving the reverse way to that desired. I continued polishing, and in 10 or 12 hours the glass was polished all over. I believe this would have been done in about three hours if I had btained rouge of good quality. It was only by using he rouge over and over again that I could advance with the polishing, avoiding adding fresh.

I now come to the process of silvering, which I have been unable to do in a satisfactory manner, and should se grateful if Mr. Purkiss can assist me in this matter. As a preliminary experiment I silvered a 6in. speenlum, nd that was everything that could be desired; the ilver adhered tenaciously to the glass, and would bear Dolishing perfectly well. With exactly the same lutions I could not obtain an adhesive deposit on my 1 speculum. Nor have I been able to produce a silver

LOCKYER.

[362] SIR,-It is very desirable that those who
assume the duty of popularizing science should, in
doing so, confine themselves to facts and avoid all mis-
representations and erroneous statements. I regret to
find that this is not always the case. In a course of
lectures on Spectrum Analysis, delivered in the year
1868, before the Society of Apothecaries, by Prof.
Roscoe, and published by Macmillan & Co., it is
stated at page 22, by way of apology for Sir Isaac
Newton not having discovered the spectral lines, that
"Newton did not observe them; and for the good
reason that he allowed the light to fall on the prism from
a round hole in the shutter. In this way he did not ob-
tain what is termed a pure spectrum, but a series of
spectra, one overlapping the other, owing to light
coming through different parts of the round hole.
he had allowed the light to pass through a fine vertical
slit; and if this slit of light-if we may use such a
term-had then fallen on the prism, placed so that the
edge of the refracting angle is parallel to the slit, he would
have observed that the solar spectrum is not continuous
but broken up by permanent dark lines. Dr. Wollaston,
making use of a fine slit (1-20th of an inch wide) of
light, discovered these fixed lines in the solar spectrum."
Before proceeding to show the erroneousness of these
statements of Prof. Roscoe, it may be well to point out
similarly erroneous statements made by Mr. Norman
Lockyer, in a course of lectures, delivered by him before
the Society of Arts during the winter of 1869. In Mr.

If

ing "It has been found by experiment," give the experiment in full and simple language, and in giving typical examples of the classes of compounds, take the simplest and not the more complex? The whole résumé on "Crystallography" might have been advantageously omitted. The question of isomerism might very easily have been explained without any reference to the elaborate memoirs of Roscoe, Berzelius, and Rammelsberg on vanadinite, apatite, and mimetite; this kind of discourse and reference to Nature and the Chemical News, will only tend to disgust and dishearten and not instruct. One of two things is obvious-if the articles are intended for such as read Nature and the Chemical News, then they are superfluous in the MECHANIC; if, for more elementary readers, then they are too loose and diffuse. I would not have Mr. Davis sacrifice anything of scientific language and accuracy to anything like a popular discourse-that would be going to the other extreme. With every good feeling let me advise Mr. Davis to take up definite points and explain them fully, but on strictly scientific principles, defining everything sharply and accurately, then his chapters will be of great value both to the lone plodding individual and to the classes reading Chemistry" throughout the country during the winter. But if the teacher has to warn his pupils against such and such statement in the MECHANIC it becomes awkward. From what I know of Mr. Davis I think we may expect good things from him, as his experience increases. In conclusion, let me remind him and your chemical readers,'

612

of one serious oversight-the word radical, throughout both chapters is spelled radicle; the latter would be correct enough in botany, but not in chemistry. ROBERT E. H. GOFFIN.

MARANTA ARROWROOT, ETC. [364] SIR,-The representation of Maranta arrow root which appeared in the ENGLISH MECHANIC, p. 498, was drawn from a sample, given me by a microscopist as genuine maranta, and as the plate was drawn by camera lucida there is no error I am convinced. On turning to Brande's "Dictionary of Chemistry" I find a representation of West Indian arrowroot, and that differs only from mine in having the rings much more strongly marked; the shape is the same. Hassall in his "Adulterations Detected," gives a similar plate. The Maranta arrowroot, plate, p. 493, is magnified 200 diameters, that power being ample to delineate most

starches.

I enclose a drawing also magnified 200 diameters of

and turmeric (a).

a sample of pure mustard, showing wheat starch (b) Will "J. C." kindly mention the works, the plates of which I might possess or procure, from which he states

he drew his information?

I am afraid if "Young Photo" tries to precipitate an ordinary old cyanide plating solution with common salt (T. W. Boord's process) he will not meet with much success, sodium chloride will not precipitate silver in solution as the double cyanide.

HYDROGEN LAMP.-"F.R.M.S." can purchase for 1s. the platinum at Griffin's, to fit in the thimbleshaped socket. If nothing else is wanting, when the hydrogen is turned on to the dry platinum it ought to ignite.

NITRATE OF SILVER (4676).-" Paddy" must mix the precipitate with carbonate of soda, and strongly heat either in a crucible or in a deep cavity on charcoal; the resulting silver must be dissolved in nitric acid and crystallized.

SCIENCE AND ART EXAMINATIONS (4699).-" Crow Trees" must be thoroughly acquainted with the organic portion of Fownes and Miller, and the contents of Bunsen's" Gasometry," Liebig's "Organic Analysis," and Ganot's "Physics." The Government examiner recommends that the candidate should digest the contents of Watts's "Dictionary" in addition.

(4706).-Has "In a Fix" got any cyanide in the water? Salt will not precipitate silver in the presence GEORGE E. DAVIS. of an excess of cyanide.

AN UNKNOWN COAL-MEASURE FOSSIL.

sented to the eye is tolerably level, but at the points
marked A A, there are considerable elevations, as if
for the attachment of muscles; and the external
borders of the bones, extending from A to the extre-
mities, are strong, the maximum thickness being about
gin. The bones somewhat resemble in form the sup-
posed opercule of the supposititious fish Archichthys.
They are not much unlike the maxilla of Megalichthys
(the Parabatrachus of Owen), but they differ from both
these in the curve of the inner edge, in the greater
thickness of the bone, in the solid protuberances near
A A, and in the longitudinal striations which cover the
surfaces of the bones in a manner resembling the
striations on the carpal bones of Gyracanthus. Upon
the slab bearing the two unknown bones there are
scales of Megalichthys and Rhizodopsis, but to neither
of these fish can the remains be ascribed.

I forward this communication in order that any coal
measure paleontologist who peruses your periodical
may be enabled to compare the specimen with the
fossils in his possession.
T. P. BARKAS, F.G.S.

[865] SIR,-The pages of Vols. I., II., and III. of Scientific Opinion contain many letters and papers from my pen on the subject of Coal-measure Paleontology, and especially on that department of paleontology which refers to fish and reptile remains found in the collieries of Northumberland.

You will perhaps permit me to direct the attention of your readers to two bones which I have recently obtained from the Northumberland

Low

Main Coal

stratum. They

to

SQUARING THE CIRCLE.
[366] SIR,-In the correspondence on the
"Rectification of the Circle," allusion is made
to the ratio 22-7, which, like 8-1416, I suppose
is the result of a process of approximation, and
I would, therefore, wish to ask:-

1. Would the result of any geometrical de-
monstration be objected to simply because it did
not exactly agree with the latter, so universally
recognized as true viz., 8-1416?

2. Has any one ever attempted to subject the excess of the square over the circle to a similar process of approximation, and if so, with what results?

My reason for putting such questions is, because I have a method of solving the problem geometrically, but the result is in excess of 3.1416 and less than 22.7, and if the answer was favourable I might be induced to publish it, as I feel It convinced it is the true geometrical ratio. would, though, put me to a little trouble to G. H. reduce to a system, &c.

IRIS DIAPHRAGM [369] SIR,-Three weeks since I w to query No. 4493, but as the letter has e serted I repeat in reply to "Unit," that ha "Iris Diaphragm" described in the Neti chester Literary and Philosophical ce in Mr. Darby's Astronomical Observer; i drawings are given of the details of noticed that "F.B.A.S." (317) deseries of the diaphragm, but I may tell "M figure is almost perfect, and that in 2 The instrument described by Mr. rays are caused when bright stars and ingenious, but I fear would be quite would probably take the form of the apres nomical work, as the image of the end pentagonal. The principle involved in has been long known; but I am not av Messrs. Beck than those I refer to. description of the adaptation for sci adopted it to their microscope, but I fe have superseded its use by another re ciple to that shown in (259), and made i and the fiques The blades are numerous, but not so regular as that formed by inher and would, most likely, cause rays from is a instead of clear discs.

The only disadvantage of india-rubber is t cays in course of time, but can of course be r required. The diaphragm should never be sin become frozen, and the more it is used the le will last. The full aperture may be used as closed entirely, and by the simple machinery I he scribed may be worked from the eye end of the teles and this is the chief advantage of the apparatas. A. BROTHERS, F.R.L.S.

Falshaw, Wilmslow.

SCREW PROPELLING.

[370] SIR,-I hope the Rev. E. Kernan will not fee! vexed if I add to the names of those connected with the history of the propeller, one not less deserving than the rest to be mentioned amongst the certain facts" I mean that of Josef Ressel, the Imperial Woodward at Trieste. In his treatise on the Archimedena screw, as annexed to his petition on 28th Nommber, 1826, for the [367] SIR,-In one of your June Nos. a method grant of a patent, showing, I be an earlier date is propounded of squaring a circle, which has been than that of Captain J. Ericsson, and declaring a new sufficiently anatomized and is clearly wanting in exact-invention consisting in propelling vess of sex, and Had the writer, however, made the basis of his even in rivers, by means of a wheel resembling an en paddle-wheels of steam-boats, and the placent triangular sections infinitely small it would have been less screw, he says "the troublesome noise caused by the correct theoretically, as the following calculation may oscillation inherent thereto, and also the waste d tend to prove :-For, let A B C be one of these sections, The circle will then be power and time in working the same, induced me to contrive an apparatus free from such defects. 1 with base B C infinitely small. adopted the theory of the screw and gave the motor of and I think it the vessel the form of a screw, advisable to fix the wheel at the stern, since the back water of the ship might promote its action." May the above suffice to explain the claim!

ness.

A

B

circumference.

Rad.
2

circumference and

No. 2

the

I trust may prove useful:-A A A is a frame made beech wood, with a bead run all round the inside fro edge. There is a slot in one of the uprights A for are, I believe, new smith. It is the invention of Mr. J. B. Smith, bar D to work in. BB inside frame, with two iron rod science, and foreman of the smith department of the Harlem Rail- C C working through guides to keep the frame true; D is a bar of beech hinged at E; F is a piece of iron whether new or way Works (U.S.). not,they are as yet It is made from gas-pipe, and of size according to lift the frame up and down; G is a thumb-screw uninterpreted by the work required. The process is as follows:-One tighten saw; H, saw; I is a connecting rod from the the best palæont-end of the pipe is made solid for the thread, while the bar D in the crank J. On the mandrel there is a table ologists in England, other is prepared for the bottom end of the rod, and to lay the wood on, not shown. The whole is well put several holes are made in the side of the pipe in which together, and stained over the same as a new plane. to insert the lever for turning the buckle. Fig. 1 repre- is a bolt to bolt it to the lathe-bed. sents the outside view and the holes for lever; Fig. 2 gives a sectional view. Compared with the usual buckles, which are expensive, and require the hand of an excellent workman, it is very cheap, its cost being KAPPA. at least 624 per cent. less than the ordinary method.

several of whom have examined them.
The forms of the bones and the positions in relation
to each other in which they lie upon the slab of shale
to which they are attached will be best understood by
reference to the annexed outline sketch, which is one-
half the natural size of the specimens.

The length of each bone is 53in., and the width of
sach at the broadest part is 2in.: the surface pre-

W. GREENWOOD.

DIVISION PLATE.

[372] SIR,-Your correspondent "Wahsrof " has been kind enough to send me one of Mr. Baker's

fore, a source of heat, and that we

Let the liquid acid be confined in a sorbi
or boiler, and thence made to pass (by a foun
through a coil of copper piping casing the se
nally. After passing through these pipe t
to the boiler. It is evident that cirenlat
these pipes it will absorb heat from the TAA
and maintain itself at the same temperate
force of some 800lb. per square inch.
all that is requisite to furnish a gas with z
carbonic acid be used for this purpose, to..
other gas which liquefies under pressure.
above though, for several reasons.

He admits the first, viz.:-the reediness of t

the harmonium, only urging that in this respect seat
readily admit. He says himself, "this doubtless is ter
harmoniums are not quite so bad as others, ED İ
But since he
chief objection to the harmonium." I thought
and hence placed it first.
agrees with me on this subject it seems strange ↳

not concede the point without hesitation.

Mr. Nash thinks my second objection, about the la to reply to it in a much more unfair manner. W. B. "on the large harmonium the division of the overpowering the treble, unfair, yet does not capt into treble and bass renders it entirely the own fault if he suffers his right hand to be over by his left." From which it is to be presumed means that by using two or three treble stops one bass the treble may be made predominant. is based e not Mr. Nash see that his defence admitting the very indictment I make ag harmonium? Why is it that two or three sets of me in the treble require to be used against one & feda the bass does overpower the treble? Bat no stratagem d in the bass? Is not this the best possible patt the kind really overcomes the radical defect of the s equality existing in any single set of harmoniam reeds all through the register. It is easy to make up a questity of tone in the treble by employing more stops than in the bass, but in that case the quality of the treble and bass are different. Yet more, as regards the treble itself, the objection is not removed but only carried an octave or two octaves higher; the alto overpowers the treble and the tenor overpowers the alto, for the simple reason that every note down the scale is relatively more powerful than the one above it. Mr. Nash concedes that the objection is just against any harmo nium with a single set of reeds. It must therefore necessarily exist against any larger instrument combining a number of such sets of reeds.

The sketch requires little explanation. A in. round bar of iron is bent into the shape shown; the step, S, is about one foot from the ground: through the top of the bar a gin. pin, P, is passed, on which it should swing, pendulum fashion. To fasten it to the bicycle, remove the pin which carries the brake, enlarge the hole to gin., then insert the pin, P, and fasten securely with the nut, N. This pin, P, will then carry the brake as well as the step. When travelling, the step is held up parallel with the hind fork by means of a spring made of a piece of in. india-rubber tubing, one end of which is fastened to the hole, O, in the bar, and the other to the top of one of the upright springs which carry the saddle spring. To use the step, move the bicycle till the off treadle or crank points upwards, then press the step down to the ground, place the foot thereon, and quietly throw the other over the saddle on to the off treadle, press upon it, and when the bicycle moves forward (not before) remove the foot off the step, which will then spring back and upwards to its place, parallel JOHN C. FRANK. with the hind fork and quite out of the way of any

CARBONIC ACID GAS AS A MOTIVE POWER. [880] SIR,-The use of carbonic acid in one shape or another has often been suggested as a motive power, and for some years I have been working on its application in the liquid state as a motive power for submarine vessels. Illness now prevents me continuing them, and I fear I shall not again be able to go on with them. May some reader of the ENGLISH MECHANIC carry out what I am unable to do; but for a nobler purpose than that of warfare-viz., the lifeboat. Anybody will understand the advantage of placing in a lifeboat a means of propulsion of 20 to 30 horse-power, and this is quite practicable by using carbonic acid. This gas under a pressure of about 800lb. per square inch becomes a liquid. as water, requires a certain If it This liquid, the same amount of caloric to reconvert it into gas. gets this heat from the atmosphere its evaporation We want, therewill soon become comparatively slow, and the tensile force of its vapours low and useless.