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is holding is an extra brake, by means of which the
engine can be stopped at 10 yards' notice. Its greatest
speed on the high road is 20 miles an hour, and in town
10. The coal and water are kept on either side of the
boiler. The carriages in construction are just the
same as any other railway carriage, with the excep-
tion of the wheels, which are as already described. It
is the invention of a gentleman named Lormargot.
H. GARLAND.

READINGS FROM THE GLOBES.-III. Sin.-Frequent allusions are made to the different constellations of the heavens both by ancient and modern poets, and this arose not only from the custom amongst all nations of making use of figurative language, but because the sowing and reaping of corn and agricultural productions depended upon a right observation of the rising and setting of particular stars. When, for instance, the sun had reached the Tropics, or turning points, it was necessary to reckon so many days before it was advisable to undertake particular work, but in these times of accurate computations and astronomical observations, the calendar is employed, which is much simpler. Thus, the poet Hesiod in his Works and Days" makes mention of the Tropics, and the Roman poet has constant allusions to the signs of the Zodiac.

nearer to the sun by 4 millions of miles in winter
than we are in summer, and, consequently the warmth
of o ur summer arises not from our proximity to the
sun, but from the fact of his being longer above the
horizon and his rays, owing to his altitude, darting
less obliquely upon the inhabitants of the North
Temperate Zone. These maps show the situation
of the earth in his orbit for every ten days, as well as
what sign of the Zodiac he is in, and should be pos-
sessed by those desirous of accurate notions upon this
subject. Thus it appears that the sun's longitude is
really the distance which the earth travels in her
course round the sun, which, computed in miles,
will be found to be more than 65,000 miles per hour.

to cool the meal before it enters the bolter; it will be seen by this that a miller cannot keep his ground mea! by him for two or three days to cool, unless indeed be has extra silks to dress it up with. 3rd. There is another matter that is against them, namely-not being able to change any number of the silk and put another on in a few minutes, according to the stuff that wants dressing and the time of year, as of cour for damp wheat meal the silk should be coarser than for dry foreign wheat meal. To obviate this I have, in conjunction with some parties in Manchester, brought out a silk machine that occupies a great deal less space thau the present silks, and any sheet may be take and another put in in a few minutes. 4th. In dressing with a silk bolter it is impossible to get the bran a clean and bright as by dressing it with a wire machine Consequently I generally put a small machine to take the bran out before it enters the silk or after it leaves it, as by that means everything is cleaned up as well as possible. 5th. By dressing with the present silk hemis-bolters there is not more than one-third of the silk that actually dresses, as the rails or ribs inside the reel as it revolves carries the head up and drops it on to the silk near the bottom at the opposite side of the reel. It is this that forces most of the flour through the silk, but it at the same time gives the silk a sudden twitch, which of course is injurious to it. E. DAVIES.

earlier

T. S. H. P.S-Mr. Dyer states the following sentence in Letter I. to need correction : "As the globe turns on is axis from west to east, those who live in west longitude, must have their time than those living in east longitude, because they will not come in to the enlightened phere so soou." He says the word "earlier should be "later." I submit the sentence must stand without correction. Turn the globe on its axis from west to east, England will come into the enlightened hemisphere sooner than America, which is in west longitude; but the time in America is earlier than in England, for when it is 12 o'clock at Loudon In order, therefore, to enter into the beauties of these noon, it is 7 o'clock in the morning at New York; so writers we should have accurate notions of the course that we come into the enlightened hemisphere sooner of the saw through the Zodiac, and it will be our busi-than the Americans, and yet their time is carlier than ness in this letter to show by the globes the longitude ours. They in the latter part of the sentence must and declination of that bright luminary as he proceeds be connected with the nominative of the sentence. in his round. It is not our purpose now to enter into auy argument either for or against the Copernican system, as this has been amply discussed, but merely to illustrate certain phenomena which can be explained on either supposition-namely, that the earth moves round the sun, or that the sun moves round the earth, and to illustrate the better, we will make the latter supposition. The figure is a representation of the two outer circles on the wooden horizon of the globe,

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TO MILLERS.

The remarks of

SIR,-I am glad to find an improvement in the letters
respecting mills and millering.
C. M.," on the balancing of stones with Clark and
Dunham's patent, I consider good sound reasoning,
and I hope we shall hear again from him. Also J.
Botting's remarks on the swish in stones, are interest-buy
ing and true. I having tried the same remedy for simi-
lar evil and corresponding results. R. R. Smith gives
us some useful hints botimes. I hope all our dusty
brethren, who have a little useful information, will
please send it to our MECHANIC for the common
benefit. I will just ask the above, or any other, if
they can give me a good remedy for filling up broken
joints in millstones; I have tried alum and borax,
but cannot make a good job of it.

E. O.

SIR,-I cannot say I am prepared to dispute Mr.
Evans' theory that the cause of a stone's standing
and running balances differing is "The balance weight
does not coincide with its counteracting object in its
radial distance from the centre," but in my blindness
I cannot conceive why it should not. He asks me if I
cannot alter a stone's standing balance by raising or
lowering the weights when running. I have already
said I have found when a stone's standing and run-
ning balance do not coincide, something was wrong,
independent of the balance; but whether it would
alter or not if both balances coincided, I am not pre-
pared to say, but to my unenlightened intellect it
seems improbable. But in spite of Mr. Evans' scien-
tific reasons why, and my inability to dispute them,
some very ugly facts (to the contrary) stare ine in the
face. And as Mr. E. says "Facts are stubborn
things," I ask both him and Mr. Smith how we managed
to balance our stones so that they "hummed like a
hive of bees," made bran "like a bee's wing," and as
good a per centage before we had the patent balauce
as we do now with it, and why every serious fault that
occurred then will now, in spite of balance. And as to
despising the standing balance as virtually of no
use, and practically non-effective," that idea has
recently done serious damage. If it be of no use, it is
mysterious how we managed to make our stones work
as well without the patent balance as with it. I
repeat the fault of a stone's dragging lies either in
empty cogs or their pitch circles not meeting, or irons
not working parallel with the face, or unlevel bed-
stone, or faulty face. Of course the running balance
will keep a stone from vibrating (?). I know of stones
that have received a good running balance, but went
empty, and on being freed by the spoutsman, com-
stopped knocked off 12 months' wear of skirt.
menced kicking violently, and before the mill could be
was the running balance that it did not keep them
steady? What was the cause of it? And why did it
not occur when being balanced? The more untrue
the face, irons, &c., are, the greater difference there is
in the two balances-so great as to drag off the skirts
when starting and stopping if the running stone has
a running instead of a standing balance. If, as Mr.
Evans asserts, the cause of the difference in the two
balauces is owing to the unequal specific gravity of
the burra, or because the balance weight does not coin-
cide with its counteracting object in its radial distance
from the centre, how is it we often see parties try the
running balance of their stones every three or four
dressings, and find it differ each time? To me it looks
very much like a different face to the running stone.

Where

COMMERCE AND TRADE. SIF-As this subject has been opened, and is one which, directly or indirectly, is of vast importance to us all, it may be as well to say a little more about it, especially because its very vastness involves the consequence of very partial views being caught of it ligent people, are captivated by that delusion, "proby most minds; hence it is, that so many, even inteltection to native industry," which is now set forth under the disguised, but equally delusive, form of reciprocity," or in other words, refusing to buy cheap what we want, because those from whom we have not sense enough to buy of us, what we offer them cheaper than they can otherwise obtain it. This is the very delusion by which "F. W. M.," page 257, is somewhat afflicted. He does not see the whole bearing of what he says. Let us accept at its worst the result he sets forth. "Our men are compelled to emigrate in large numbers." What of that? A temunmixed good to them and all-they leave a country porary suffering to them and others-a resulting overstocked with labour, where, if they cannot produce, they are a burden on the producers; they go away, and at once become producers to their own great benefit, and large customers to those who remain behind.

Rightly considered, the necessity for emigration is a great proof our prosperity, for it means excess of population, but an excess not due to diminished work (for any intelligent man knows that the total work of the country is vastly increased every year), but to the rapid ratio of increase of population, and to temporary changes in the nature of work, which at times throw out whole classes of workmen, who are then unable readily to find fresh work, not from its deficiency so much, as from the competition that involves with those Now nothing is much more already engaged in it. certain in political economy than that a rapid increase of population is a consequence of prosperity. Staguant nations never increase-they very commonly decrease in number, and this is only one form of Nature's universal law, that creatures only multiply where there Even one year's bad trade, or disaster, is marked by diminished birth rates in the next, as well as increased death rates.

is food for them.

Of course it is hard to look beyond the immediate personal action of these laws, and hence it is that so intelligent a race as the Amerieaus violate them. Instead of recognising the unlimited advantages Nature gives them, as producers of raw material, they wish to do everything themselves, and seek to be manufac turers, which those very advantages forbid, by their effect on the labour market. The consequence is, that while a few years ago they were dangerous competitors in every market, since they adopted their tariff system, we are beating them everywhere, and literally driving their flag off the seas. I quote the following from the "New York shipping and Commercial List":"No better commentary upon the decay of American navigation interests can be had, than is afforded in the fact that the Novelty Iron Works have sold off most of the machinery and tools; the Allaire works are now occupied as a stable; the Etea Iron Works have ceased to make marine engines; the Fulton Iron Works are for sale; W. H. Webb's shipyard is to let: Henry Steer's yard is empty; the Continental Iron Works are almost deserted, and grass is growing in nearly all of the shipyards which a few years ago were filled with workmen." It may be said, that something similar applies to London, but that is only because other English ports are taking the trade. English shipping is superseding American, and there is no other reason than this -America tries to make her own iron, &c., which she cannot, except at high price, instead of buying ours cheap with the corn and other things she can really produce well, and thereby indirectly throws away the friendly union with us which would result from being mutually necessary to, and benefactors of, each other.

and the eclipse may represent the ecliptic on its surface. The sun's longitude, then, and indeed of any other celestial body, is its distance from the point Aries eastward. It is from this point that the reckoning begin, and it will be found from an inspection of the figure, that he is at this point on March 20, he then passes through the signs of the Zodiac as they are marked in the circle, and reaches them on the months immediately above them. Thus the sun enters Cancer, June 21, and generally speaking he enters a new sign on the 20th of each month; that is, apparently enters, for the stars being millions of miles distant from both the earth and the sun, his entrance into them is obvious to the eye only. Concerning the origin of the names assigned to the signs of the Zodiac, there seems to be some uncertainty, but it is generally supposed that they are intended to denote the peculiarities of the season at hese particular times. Thus he entered the signs of the Ram and the Bull, when farmers were busy in rearing domestic animals, and at his greatest height, he begins to recede, or, like a crab, to walk backwards. The Lion being a native of the Torrid Zone denotes the heat of the season, the Balances when the days and nights are again equal, the Archer, the hunting season, the Waterbearer, the watery aspect of the clouds, and the Fishes that the seas were open for mans supply when the ground was hard from frost, and uncultivated. The declination of the sun means his distance north or south of the equator, his greatest declination being 2340, when he has reached the meridian line on which the angle is measured, which the ecliptic makes with the equator, and he then shines over the North Pole, and 2340 beyond it. But to this subject we shall have sun's longitude by the globe, we have only to look on the wooden horizon for the month, and the corresponding circle beneath will show the sign, and if we wish to know the declination we have only to bring the sun's place to the brazen meridian, just as we find the latitude of a place, and immediately over it is the declination. We may remark that the orbit which SIR, F. W. M.," on page 257, eeems to have fallen the sun makes, or the earth, for it is immaterial for SIR,-Having in my letter in this week's issue of the into the trap that "Saul Rymea "laid. He believes our purpose, is not circular, but elliptical, and those ENGLISH MECHANIC endeavoured to show that a silk that England is getting drained of her wealth, by an who wish t pursue the subject will do well to study bolter must make a better or finer sample of flour than outflow of money sufficient to make our exports balance Mr. Proctor Maps, published by Messrs. Longmans, a wire machine, so that, after showing the advantages our imports-a very common error. It is necessary where they will find not only the orbit of the earth, of said bolters, I will now describe some of their dis- to remember that, with the most insignificant excepbut the orbit of all the planets round the sun accu- advantages. In the first place, owing to the great tions, trade is barter; the fluctuation in the amount rately described according to scale. By a study of length they have to be made to dress from, say, even of gold held by England from year to year, may be these maps it will be seen that the sun is in perigee four pairs of stones is very much against their adop-entirely disregarded in examining her trade with the or nearest to the earth in winter, ten days after he tion in many mills because of their taking up so much whole world, and this one fact should be steadily kept has entered Capricorn, December 31, when, according room. 2nd. As they will not, generally speaking, in sight, that one year with another, the goods we to Mr. Proctor's scale of measurement, he is 91 dress more than from three to five sacks per hour on send out to the foreigner, are considered by him equal millions of miles from the earth, and that he is in an average, or about one-fourth the quantity a good in value to what he sends us in return. Take the case apogee, or at his greatest distance from us, in Mid-wire machine will dress, causes them to be worked that I gave, and which "F. W. M." holds up to summer, July 2, when his distance by the same scale continuously as the mill grinds, and there is often fixed ridicule. I send out a cargo, which costs me here as 95 millions of miles. Thus we find that we are over the head of the machine a hopper boy or cooler, £18,000, but when it reaches the foreigner, it is worth

afterwards to advert. It, then, we wish to know the

A STONEMAN.

[Will some miller, or any one else who may know, tell us how we can get the names and addresses of the millers of Great Britain and Ireland?-ED. E. M.]

SIGMA.

€24,000 to him there; and in return he ships to me a cargo, for which he charges me there £24,000; by doing so, he balances my account, I owe him nothing, he owes me nothing; but his cargo, when it reaches me, is worth £29,000 here. I do a good trade, and can afford to pay freight, insurance, &c., out of the difference of the English values of the two cargoes. Where the goods are, makes the difference in value. HERBERT.

INDUCTION COIL.

SIR,-I do not quite apprehend Mr. Cunningham's question, p. 258. Covered wire is used simply for convenience of manufacture, but any mode of keeping the wires out of contact answers. When I first took up the study of electricity, I could get neither books nor materials, and had to study out things for myself, and discover them afresh, guided only by the knowledge that certain things had been done. That was in Australia, before the days of gold; it was also before the days of Rhumkorff's coil, and I made to all intents an induction coil (only without the condenser) without knowing that I had done something new, for my coil gave violent shocks by holding one conductor only. The reason was that I had no covered wire, and invented a substitute, and my wire was exceedingly fine; in fact, I laid it very closely and evenly, separating the turns by a cotton thread, saturating very carefully with an insulating varnish, and diviing the layers by silk saturated with the same. But such a coil, though very well for an amateur experimentalist, would be very troublesome to make, and almost incapable of repair if injured, and consequently would not have been made in any but such exceptional conditions.

No doubt Mr. Cunningham's coil acts as he says; the only point is, whether, with the same battery power, much greater effects would not be obtained from the same wire if the interposed material were absent, for the true point to be aimed at is to keep the wire as close as possible to the magnetic core, as distance has so great effect in diminishing action; the only limit to this approximation being the necessity for insulation. The moment this insulation exceeds what is necessary, it is injurious, by weakening the effect; hence the importance of using the very best insulators, and applying them on the best principles. Taking, for illustration, a coil 6in. long by 3in. diameter, the secondary of which is an inch in depth, if we use the common process of working the layers from end to end, the points of extreme tension are separated only by that inch, and it being occupied with a succession of stages of wire, there is great facility offered for the spark to leap across this space, and we must resist this by extreme care in insulation; but if, beginning at one end, we work our layers in sections instead of strata, and complete the coil as we go towards the other end, the points of extreme tension are separated by 6in. instead of one, and much less perfect insulation is needed. There is, however, a great practical difficulty in the way, and at present a compromise is effected by the process of dividing the secondary into a series of short independent coils, each complete in itself, and connected to its neighbours. This will reply to Mr. Forbes, No. 3953. The connections are made alternately by passing an end under the disc to form the commencement of next section, and soldering the outer end. The Mercury Break is only needed for very powerful coils.

SIGMA.

I

panded band which appears when denser hydrogen is
employed." This paper is dated April 13, 1868, and L
think it was after the eclipse of 1868 that the alliance
referred to above was formed. But the discovery is
older yet. We must not overlook the work of Miller,
Huggins, Plücker, Angström, Gladstone, and the host
of other eminent men who have advanced the cause of
spectroscopic science.
RICHARD A. PROCTOR.

SATURN.

SIR,-The reviewer of my work has treated me so kindly that I hardly like putting in a word in favour of the view to which he feels compelled to "demur at once." I object, myself, to startling theories unless put forward to explain even more startling facts. This is the case as regards my theory about Jupiter and Saturn.

tions to build a trial steam lifeboat, and among the
list of subscribers such corporations and institutions
as Lloyd's.the Salvage Institution, the Shipwrecked
Mariners' Society, and the Royal National Lifeboat
Institution, &c., I was much surprised to see in your
Impression of the 27th ult. the letter from Mr. Lewis,
secretary to the last-named institution, raising such
objections, many of them ridiculous on the face of
them. Surely the several institutions here named, and
more particularly the Royal National Lifeboat Insti-
tution, thoroughly examined the plans, models, and
drawings, and fully satisfied themselves that Capt. STARTLING THEORY ABOUT JUPITER AND
Petersen's invention was not only practicable, but had
every chance of success. I doubt not Mr. Lewis raised
the same objections at the time his committee was in-
specting the invention; and the explanations given
by Capt. Pesersen were such that they were perfectly
satisfied it could be carried out, and expressed them-
selves as such by granting £100 (about one-sixth of
the amount required) towards building a trial boat.
In order to show the absurdity of these objections, I
will just quote one, in which he says-That the
Any theory which accounts for the apparent advance
motion of boats, under such circumstances, is so great
of a satellite on the disc of Jupiter and its apparent re-
and violent, they sometimes standing perpendicular, turn presently outside the disc (an observation made-
with either the bow or stern uppermost, that the pro-independently by three such astronomers as Smyth,
peller would work at a great disadvantage, and the Pearson, and Maclear) must, I apprehend, be rather
machinery be perhaps liable to disarrangement."
striking. I think mine the only available one. In
Now, it is self-evident that when this happens, the fact, I cannot imagine any other. I by no means assert
same objection would apply to the lifeboat now in use,
that the surface of Jupiter was necessarily changed in
inasmuch as the men in the boats would, under such shape on this occasion. Clouds suspended at a great
circumstances, be placed in an horizontal position; height in his atmosphere may have suddenly been dis-
but Capt. Petersen's steam lifeboat would have the ad- sipated. Again, Saturn's assumption of the square-
vantage, for I see by his plans that he carries two more
shouldered aspect seems to me wholly inexplicable on
sets of oars than the present boats, in addition to which any other hypothesis than mine.
he has the steam propellers. This advantage is ob-
tained by the difference in the formation and arrange-
ment of the air-chambers, &c.

Mr. Lewis must be wrong in sayin g that "most of the plans merely aim at putting an engine in one of our lifeboats," for from what I have seen and heard of the drawings and plans of Capt. Petersen's selfrighting steam lifeboat, I am under the impression that it is of a very different form, construction, &c., giving as much, if not more, room than those in present use.

I will not trespass further upon your valuable paper. as I have no doubt Capt. Petersen will fully answer all the objections, to the complete satisfaction of the subscribers to the ENGLISH MECHANIC Lifeboat Fund; which fund I hope may be a success, and that their boat will be built in accordance with Capt. Petersen's plans, which I believe are the very best extant.

REBUILDING A CHURCH ORGAN.

R. S.

SIR, I am thinking of rebuilding our church organ: adding a swell and independent pedal organ and I should like to know what the dimensions of the bellows should be for a liberal supply of wind, and yet no larger than can be helped.

I should have three 8ft. stops. two 4ft., one 2ft. in great organ; two 8ft., two 4ft. in small organ; one 16ft. tone (8ft. stopped) in pedal organ. I have most of the pipes by me: and the pedal pipes are gedact, with a foot of 3in. diameter in the aperture for the CCC. If any correspondent would give me dimensions for bellows and reservoir I shall be extremely obliged: also, is there any real practical advantage in having three feeders worked by a three-throw crank, over the usual two feeders worked by a lever? Theoretically it seems best; but is it?

COUNTRY PARSON.

DARK LINES IN THE SOLAR SPECTRUM.

SIR-I could hardly believe that Mr. Lockyer had not misread my letter at p. 211; but on referring to it I found I really had by a lapsus calami spoken of density instead of quantity. You know how much I have been overtaxed with work lately, and will therefore understand how easily such a slip would occur. Fortunately, however, the text exhibits my real meaning very clearly; and I have written too often and too recently (see Pop. Sc. Review for October, 1869, in which I have introduced even a picture of the widened line of hydrogen, as also my "Other Worlds," at p. 46) to a contrary effect for any question to exist as to my knowledge of the fact pointed out by Mr. Lockyer. In the letter he quotes, I was showing that the atmospheric dark lines could not change in thickness as the sun neared the horizon, notwithstanding the greater range of atmosphere through which the solar rays then pass. No one knows better than Mr. Lockyer that this is the case. A ray from the sun might pass tangentially through the earth's atmosphere fifty times and yet the atmospheric dark lines would be no wider than in the spectrum of the sun in the zenith.

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Sir John Herschell writes to me of this theory, Strange as it seemed to me at first, I cannot but admit that the reasons you adduce are not to be lightly set aside.' R. A. PROctor.

"

AMALGAMATION AS A PREVENTIVE OF RUST. SIR,-Some time since I sent a query to our paper on preventing rust. It was not, I believe, answered. I now send a clipping on this subject, which may be interesting to others as well as myself:-" Reinsch, of Germany, proposes the amalgamation of the surface of the iron as the best protection against rast, the only difficulty being to make the mercury adhere to the iron. It is well known that iron has no affinity for mercury, and even a perfectly clean surface, when rubbed with metallic mercury, will absorb none of it. On the other hand, gold, tin, lead, and several other metals will take it very readily, and almost all metals quickly become coated with mercury when plunged into a solution of a mercurial salt; but iron and steel resist even this treatment, and it is only here and there that some traces of the mercury adhere. Fortunately a method of causing the mercury to adhere to the iron bas at last been discovered. The iron is first well cleaned with hydrochloric acid, and then plunged into a very dilute solution of sulphate of copper, mixed with a little hydrochloric acid. It immediately becomes thinly coated with metallic copper, which copper must be removed by means of a brush, friction with paper, aud washing. The iron is then placed in a very dilute solution of bichloride of mercury, also mixed with a little free hydrochloric acid. It becomes perfectly coated with a layer of mercury, which cannot be removed by friction with rough bodies. This mercurial covering protects the iron very well against rusting, especially if after the amalgamation it has been washed with liquid ammonia. The inventor has compared the action of the air of the laboratory, continually charged, as it is, with acid vapours, on iron objects, some of which were the latter were rapidly eaten up, as it were, the amalamalgamated and some not, and found that, while gamated objects did not show a trace of rust; and he recommends the process highly for the working parts also proposes to amalgamate the iron parts of susof all kinds of machinery, clocks, engines, &c. He pension and other bridges before covering them with paint, in order to ensure a more perfect protection; but, as we know that mercury diminishes considerably the strength of those metals, with which it easily amalthis respect on iron wire before risking the amalgagamates, we think it would be well to test its action in mation of the wires forming the cables of a suspension bridge."

plication of mercury to iron, but I see no reason why I may say that I have not practically tested the apthis method should not be successful.

J. H. W.

DRY PLATE PHOTOGRAPHY. SIR,-I have lately been making some experiments in dry plate photography, and I think it will not be out of place to give the readers of our journal a few hints on this subject, which I consider one of the most beautiful and interesting branches of the above art. Within the last two months I have tried three processes, tannin, Ryley's modified Fothergill, and collodioalbumen, but, taking everything into consideration, prefer the tannin process, as the plates can be prepared very quickly-in fact, I usually prepare two dozen in one night, and allow them to dry in the dark room until morning, when I find them quite dry without the application of artificial heat. I have used Mawson's ordinary wet plate collodion, which I find an excellent one for the tannin process. I coat the plate and sensitise it in the usual manner, and on removing the plate from the bath I wash it with about a quart of water (I have tried distilled water, but I find plain water to answer quite as well). I then immerse it in a 15 grain solution of taunin, and let it remain while another plate is being prepared. It is then taken out of the tannih, and placed to dry in racks, or reared against the wall. When it is quite dry it is varnished about in. all round with ordinary black varnish, laid on with a soft camel hair brush. It is then ready for exposure, which should be about 12 times as long as for wet plates. I develope with pyro, 2 grains; citric acid, 1 grain; water, loz. The picture should be brought out with the least possible quantity of silver in the developer, and when all the detail is ou: it can be intensified in the usual manner. to overlook any of the results he has obtained. Though I take far too much interest in Mr. Lockyer's work With Ryley's process I had very little success, but I do not by any means accept all his conclusions, and with the collodio-albumen process I have obtained indeed consider some of them to be beyond all question some very beautiful results; but it is a very trouble- erroneous, I none the less appreciate most thoroughly some process, and very liable to blisters, &c.; so on the his skill in observation, his ingenuity in devising new whole I prefer the tannin. I usually develope the modes of research (witness his suggestion in 1866 about Suppose the lever of a safety valve of uniform same evening I take the pictures. I beg to ask "Mus," the prominence spectrum) and the perseverance and depth and thickness to be 24in. long, 3in. from the fulor some other of your photographic correspondents, if energy with which he carries out his purposes. If my crum to the centre of the valve, and weighing 31b. they will be kind enough to describe to me the coffee haste in writing should ever again lead to a lapsus cal-Now it is the opinion of many that a lever of this and gum gallic processes, and let me know if they ami let Mr. Lockyer believe the cause of the mistake dimensions would only exert a pressure of 31b. on the have had any success in them, as I believe they are both very good processes; but I have not the formula. to be anything rather than forgetfulness of his work, valve. This, I must say, is a great mistake, for such I have also got an old wedding ring; it weighs just astronomy. or of any that is being done by our fellow-workers in a lever instead of exerting a pressure equal to its own weight, would exert a pressure as great as three 25 grains. I shall be glad if any of our subscribers May I venture, however, to point out that the dis- times its own weight, or 121b. on the valve, and this is can inform me how to convert it into chloride of gold covery of the influence of density on the thickness of what is called the effective pressure. solution for toning purposes. I have tried "Mus.'s " spectral lines belongs to an earlier date than Mr. Locktoning bath, and find it an excellent one, and should yer's alliance with Dr. Frankland. I think Plücker like to have a few more hints from him. would have something to say on this point as well as on the influence of temperature. I have a paper before me in which Mr. Huggins says incidentally it seemed of importance to have proof from experiment that this line of hydrogen, when it becomes broad, expands equally in both directions. I made the comparison of the narrow line of the vacuum tube with the more ex

TANNIC ACID.

RE CAPT. PETERSEN'S STEAM LIFEBOAT. SIR,-After reading in your journal of the 20th ult. an appeal, on behalf of Capt. Petersen, for subscrip

If "T. A.'s" view required further demolition, evidence might be urged which is even clearer than that adduced by Mr. Lockyer. I refer to the existence of dark lines in the spectra of the stars.

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THE SAFETY VALVE. SIR,-Having noticed many queries in our ENGLISH MECHANIC relative to the lever safety valve, I now offer, for the benefit of my brother readers, the following calculations thereon. Fig. 1 is a diagram of a lever safety valve of the ordinary construction in weight. which L represents the lever, V the valve, and W the

As the words effective pressure will be frequently met with in the following examples. I shall explain the meaning of this phrase before entering into the cal

culations.

RULE.-If the lever be of uniform depth and thickness the effect of its weight on the valve is the same as if it were collected at its middle, but if the lever is tapered, then its effective pressure can only be found by disconnecting it and ascertaining what weight is required to balance it, making the point in a line with the centre of the valve the fulcrum. The result will be the effective pressure of such a lever.

All the examples will be worked out by two methods,

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of the valve 3in., and a weight equal to 24lb. placed on the extremity of the lever. Required the pressure per square inch. In this example the lever is supposed to be parallel, and to weigh 21b., and the valve 5lb.

Let d represent the distance from A to B, C the distance from A to C, d the diameter of the valve, w the weight, p the effective pressure of the valve and lever, e the decimal 7854, and r the pressure per square inch. Then

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219912

Ans. 77 071b. per. sq. in. Ex. 2. The diameter of a safety valve is 2.5in., pressure per square inch 201b., distance from the fulcrum to the centre of the valve 3in., weight on the end of the lever 401b., effective pressure of the lever and valve 81b. Required the length of the lever.

Let d represent the diameter of the valve, e, the decimal 7854, p the effective pressure of the lever and valve, w the weight, s the pressure per square inch, t the distance from A to B, and the unknown part A to C.

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Ex. 3. The diameter of a safety valve is 3in. distance from the fulcrum to the valve 3in., effective pressure of the lever and valve 6-25lb. Required the weight to be placed 24in. from the fulcrum to te equal to 80lb. per square inch.

Let & represent the diameter of the valve, e the decimal 7854, r the ratio of A C to A B, p the effective pressure of the lever and valve, s the pressure per square inch, and r the weight required. Then

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Then

THE BOEHM FLUTE.

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dix exp - ƒ 2:52 x 7854 = 4908 area of valve. 20 pressure per sq. in. 98.160

6-762 length of lever.
10 weight on

90-160)270-480(3 270-480

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Ans. 3in.

The divisor 90-160 is obtained by deducting the weight of the valve and lever from the direct pressure 98.16lb.

Ex. 5. The lever of a safety-valve is 24in. long, 3in. from the fulcrum to the centre of the valve, effective weight of the valve and lever 625lb., pressure per sq. in. 80lb., weight on the end of lever 69 90475lb. Required the diameter of the valve.

Let rrepresent the ratio of AC to A B, w the weight, p the effective pressure of the valve and lever, S the pressure per sq. in. e the decimal 7854, and x the required diameter.

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80 pressure per sq. in.

Cy is the longitude

565 4880

SA is the declination

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The divisor 8 is the ratio of AC to A B because 3: 24: 18. Ex. 4. A safety valve has a lever 6-762in. long, a weight equal to 40lb. on its extremity, the pressure per square inch 201b., effective pressure of the lever and valve 8lb., and the diameter of the valve 2:5in. Required the distance from A to B. Let d represent the diameter of the valve, w the weight, the length of lever, p the pressure per square inch, e the decimal 7854, f the effective pressure of the valve and lever, and x the distance required.

= a

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By Q is the obliquity of the ecliptic w

S

A

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tan, d

cos. P

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A =

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SIR,-The ring principle on all instruments of the flute genus, is the same, it gives the power of closing two or more holes by the action of one finger only. The invention of this system belongs to a Captain Gordon, who conceived the idea in Paris, about thirty years ago; the application of it, however, is Böehm's a professor of Munich. I think a little work "The Flute in its Transition State," by the Hon. and Rev. H. Skeffington, would interest "Another Flautist." Hatchard, or Skeffington Piccadilly, are the publishers. As a soloist I am acquainted with nearly For the Böebm fiute I cannot say every form of flute. much; it is an expensive instrument; the faults I find with are, the constantly-recurring difficulties in executing rapid and continuous passages, especially in the third octave, arising from the cross and back fingerings. To illustrate this, the B flat, which is produced naturally and easily on the Nicholson flute, is fingered on the Böehm by placing the third finger of the left hand on the ring of the G hole, and F sharp is fingered by pressing down the ring of the E hole; these are very awkward and unnatural fingerings, added to which, the quality of tone in the third octave is thin, weak, and the notes bear very sharp (in the old flute they bear flat), and it is almost impossible for an amateur to blow them in tune. This arises from the fundamental holes being made too large, and without due attention to the part they are required to take as vent holes in the production of the notes in the third octave. But should "Another Flautist" desire still to hear more of the Böehm, I shall be happy to give him information. Tune, tone, and facility, are the things sought for by flute players of all classes, and with your permission I will now describe as briefly as I can, a flute in which these qualities are combined to the fullest possible extent As a professor of the flute, having no pecuniary interest in flute manufacture, I continued to use the Böhm because its powers and capabilities were so great, notwithstanding the toil it imposed upon the performer,especially with the open G sharp key. Nearly eight years ago, the late Mr. John Clinton showed me his flute, called the "Equisonant," a vast improvement on the Böhm, which I have used ever since. I subjoin a sketch of it, with an explanation. In the Böebm the thumb key makes C natural, in this flute that key makes both B flat and C natural. There is a small open key at a (the C natural key), which is kept shut by the thumb key, and when the latter is opened for B flat in the usual manner of fingering this note, the C natural key is kept closed by the second finger of the left hand pressing down the ring surrounding the A hole. There is also an open F sharp key at 6, which is shut by the second finger of the right hand pressing on the F natural hole ring, the third finger of the same band closes it in making D and F natural, for which latter note the "fork fingering" is used in all rugged and difficult passages. The F natural key (short) At c there is a lever for acting rapidly remains.. upon either the B flat or C natural keys. At d is a lever for the D shake key e. Your correspondent knows not what he asks; the mechanism of flutes has been a vexed and most intricate question.

SABLE.

POST-OFFICE TELEGRAPHS. SIR,-I shall be glad if you will allow me, through the medium of your pages, to ask some of your able correspondents, the following questions, which are important to many in the same circumstances as myself. It is well known that the Post-Office has lately acquired the telegraphs, and a great many postmasters have to waste hours daily in watching the instruments, and therefore I wish to know whether it is possible to fix a bell, or other apparatus, to the existing single needle instrument, ia such a manner, that we shall have warning without the watching

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diam., and -in. thick outside, and holds 18 No. 24 cotton, and the Elliptic holds 14 yards, the diam. being in., and the outside thicknessin. Wheeler and Wilson's spool is represented at Fig. 1, a front view, and Fig. 2 a section. It is formed of a pair of thin steel discs, a b, fixed on a brass axis C, with a hole through it, which fits on the shaft of the machine to receive a rotary motion for winding on the thread, and in the space between the double convex spool. A very slight variation of tension may be given by winding on the thread more or less tightly, but it is too limited to be of much use. To provide a tension on a spool, the following plan has been adopted. A pair of flat discs, with the thread wound on the axis, which also has a hole through it, is placed within a case or shell, having an axis to retain the spool in place, and to allow it to unwind freely. In the rim of the case or shell, holes were made for the thread from the spool to pass through, to give tension in the same manner as in Thomas's shuttle. There are machines of different makers working this kind of spool, but they are not successful compared with other machines, although it may be wrong to trace the failure to the spool only. In some machines, the spool was applied horizontally, as illustrated in Fig. 3, a plan, and Fig. 4 a sectional elevation; a is the spool, composed of two flat discs on an axis, with a hole through it. The shell or case b, has a centre pin, on which the spool a revolves. The thread passes from it to the holes C, and is passed through one or more to obtain the tension required. The frame d d of the machine, is bored large enough to contain the spool, and a rotating hook e secured to the pinion f; an axis, g, passes through the pinion. The top end of the axis forms the bed on which the spool and case rests, and the lower end is secured to the frame of the inachine. The pinion f is driven by a rack motion in some machines, in others the hook receives a direct circular movement. The action is as follows:-the ascent of the needle in the needle slot, throws off the loop, the hook takes it in its rotation, or its vibratory movement, and opens it, when on the back end of the hook, then carries it more than halfway around the spool case; here the needle pulls the thread off the hook, which returns ready for the next stroke or stitch. In machines which make a complete rotation of the hook, the needle thread is less liable to break, and more easily slips off the hook. When the needle thread has been passed around the spool case and released, it has to be pulled up through the needle plate at a great velocity-for every stitch from 2in. to 3in of thread must so pass. This is usually done by a spring above the needle, and the least accident to so delicate an instrument, puts the machine out of order. A thin fabric, stitched by a shuttle, compared with one stitched by a spool machine, shows in practice what may be expected from theory-viz., the less quantity of thread passed through the fabric, the better the stitch, and the longer the loop passed through the fabric, the more uneven it must appear, laying below the surface on the upper side, or drawn too deeply into it, and forming too thick a ridge on the lower side. The spool machines are not made or sold because of this quality, but because of certain other merits they possess. All the best qualities in the various machines have not been combined in any machine yet made, nor are they likely to be. This thought should humble some of the members of the sewing machine family, who are given to overmuch boasting. Little remains to be noticed about the various instruments employed in the formation of the lock stitch, until the inachines are described and compared.

Other contrivances have been patented, or proposed, but not of sufficient practical value to describe them; and some of these here noticed, serve to show the many ways proposed to do the same thing, and to point out that the impracticable may become the stepping stone to the useful; or to show inventors what has been already done, or attempted, and to save them the trouble of re-inventing and re-patenting. This has been done to a large extent, and many years' experience in searching the patents, and making new machines, and experiments for inventors, leads me, as a matter of duty, to warn those who are fond of new ideas to be careful. One of the most unsuccessful attempts to form the lock stitch, and one often attempted, is to use a large reel of thread below in a spool, shuttle, or its equivalent, so that it will last as long as the needle thread, and require no re-winding. One of the most likely plans to do this, was to place the reel in a large spool case, having an external screw, which, by rotating, carried the needle thread from its front to its back end, the holder and driver being arranged to let the thread pass over it without obstruction. The arrangement was so far practical, but it involved long needle loops. More time is lost in pulling up long needle loops than in rewinding spools or shuttle reels. The spool, laying on its flat bed, and having a horizontal moving hook, is not so well adapted to work as one vertically placed. In the former the hook in taking the thread from the needle pulls it out of its slot horizontally, and thus bends or breaks it. The vertical pull of the hook is a far better arrangement, the needle being less liable to strain or breaking; and the thread pulled more in one direction only, or chiefly downward instead of across the needle: A vertically oscillating book has been applied to carry the thread around the spol, the hook being curved to nearly match the circumference of the spool or holder. All such contrivances are more complicated than direct circular motion, and the complicated in mechanism is nearly always leading to failure; the simple, giving less trouble to learn, or keep in order, leads to

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terbalanced? If the experiment suggested be made,
it will be observed that under the blue correction,
black letters will appear absolutely blue, whereas in
the other case, the black will remain unimpaired. I
should also be glad to know what effect over and
under correction have upon the definition, and whether
object glasses, in which the extreme red and violet
are united, can now be procured, and of whom?

that where there is more than one continued wire the
current is completed in one, while in the secondary
wire another current is induced which completely de-
stroys the power as a remedial agent.
Since writing the above I have received so many
answers respecting Medical Coil ("Wanted") as per
advertisement in No. 270, that I am more strongly
convinced than ever that the apparatus and applica-rays
tion generally are totally unsuited to the purpose. The
chief error seems to be in using intense battery power
as though the living economy were to be relieved of
pain by additional torture. Most of the coils are
primary and secondary wires, and most likely have
no guide to the uninitiated as to which is the nega-
tiue and which the positive pole. It is manifest that
this latter is of the greatest importance, since in
many diseases the current from the positive element
should flow with the natural stream through the
system, whilst in others the current is reversed.
W. A.

0. G.

GEOLOGY OF IRELAND.-WHEEL-STONES. SIR,-The deposits of limestone passed over by your correspondent F. Harwood," p. 257, is that known to geologists as the Mountain Limestone, and occurs as the middle group in the Carboniferous system immeThis fordiately underlying the true coal measures, mation and the carboniferous slates are widely developed in Ireland, and give to the scenery of that country some of its peculiar and special features. The characteristic fossils of the mountain limestone are corals, and enermites, especially the latter, which very often LIGHT OF HEAVENLY BODIES. make up the entire mass of the stone; from this cirSIR,-In a letter addressed to the astronomical cumstance it is aptly termed "euermital limestone." readers of the journal in general, H. W. Bishop states The enermite, or stone lily," so called from its elethat I said" that the light of D'Arrest's comet was to gant shape, is an animal, and belongs to the class Rabe o 126.1 think I may venture to say that I never diata; it is, in fact, a star-fish set upon a flexible and said anything of the kind. What I said was, pro-jointed stalk. It is of marine habitat, and wherever bably, that the intensity of the light of the comet found as fossils indicates the strata to be of marine would be represented by that fraction. origin. Until recently the race of Orinoidea were The intensity of light of a heavenly body not self- thought to be extinct, and only a dozen kinds are now known to exist, one of the dozen being dredged up by luminous is proportioned to R and D represent- Professor Forbes in Dublin Bay. The separated discs of which the stems of these creatures were composed ing respectively the radius vector and the distance being naturally perforated, were thus easily strung from the earth. At the time mentioned this fraction upon strings and used as rosaries; they were likewise 1 called wheel-stones, and St. Cuthbert's beads, by the English peasantry, St. Cuthbert being credited with their production. Sir Walter Scott refers to this circumstance ia Marmion :

R2 D2

1

R2 D2

was equal to 0-126. At the time that the comet became invisible to Maclear, at the Cape of Good Hope, at the last apparition, the intensity was equal to 0190, the probability was therefore that at the date I mentioned, the comet would be slightly fainter than when lost sight of by Maclear. So far as I know at present, the comet has not been discovered.

THE LATHE.

OMICRON.

SIR, Since the appearance
ENGLISH
in the
MECHANIC of the description of the Saltaire Lathe, I
have been troubled with a wish which I have had
many a time during the last two or three years; and
that is to improve the lathe in my possession, or make
a new one; I have been a subscriber from the first
number, and have carefully read all the articles on the
lathe, but I am undecided on many of the different
points of a perfect amateur's lathe. Could Mr. Smith
be induced to give us working drawings of an amateurs
lathe, drawings to scale, say the gantry, so as to give
height from floor, and a section of do., length he would
recommend gantry to te, drawings of the two heads,
and height of centres, together with the form and
diameter of spindle of fast head-in fact, all drawings
and dimensions to enable an intelligent workman to
construct one, always bearing in mind all to be
made so that the other tools, chucks, slides, and the
different cutting apparatus belonging to a complete
lathe could be added to at the inclination or conveni-

ence of the workman; I think it would be a very in-
If the
teresting subject, and one very popular.
height of the centres given did not suit every one, they
could enlarge or reduce the dimensions to their own.
That the subject is of interest I see by the inquiries
of No. 3866 and 3867 in this week's number. Some time
since we had two or three promises from different
parties to give us specimens, &c., which I am sure
would give pleasure to more than myself, and also
Mr. Plant promised drawings of his chucks. I am
sure they will excuse me reminding them-the reason
is, I am anxiously expecting them.

H.

4

ACHROMATIC OBJECT GLASSES. SIR,-If any of your contributors would kindly afford information upon the following points in connection with achromatic telescope object glasses, it would be highly esteemed. In Brewster's and other works upon optics, the secondary spectrum is described as being of a wine, claret, purple, or lilac colour, on one side, and of a green colour on the other side of the focus. Now, I have had opportunities of examining object glasses by some of our best makers, and the outstanding colours in all of them, were (to my eyes) blue and yellow. Am I to infer from this difference, that the tint of such oustanding colours is chiefly influenced by the colours of the two rays selected for correction, and that the extreme red and violet ones (as mentioned in the works alluded to), are no longer (as a rule) adopted for that purpose; or is such difference attributable to the irrationality of the glass now employed? It has struck me, upon comparing one or two glasses which have come under my notice, giving a dark outstanding colour, resembling the claret, or other colour referred to, with one in the blue state of correction, that the former was incomparably superior in defining fine black lines, which I attributed to the contrast between black and white being much better preserved under the influence of a dark colour, than a pale bright one. The dark colour also appeared to be much less in quantity than the blue, which latter seemed to form a cloud before the object, and a wide fringe around it, while no such obstruction was perceptible or appreciable in the case I should like of the claret or deeper-toned colour. some of your readers to make the experiment upon a white enamelled watch face, at a distance not exceeding thirty or forty yards, in full sunshine, under a high power. Other states of achromatism may, by uniting more luminous rays, appear, theoretically, to offer an advantage in the shape of increased intensity, but is it not probable that a paramount disadvantage may accrue from the uncorrected colour being both paler and thicker, or of greater breadth, whereby the advantage which would otherwise necessarily follow the increased amount of light, would be coun

"On a rock by Lindisfarn
St. Cuthbert sits and toils to frame
The sea-born beads that bear his name."

H. H.

THE SOLAR SPECTRUM.
SIR,-I am pleased to find so good an authority as
J. Norman Lockyer endeavouring to remove my diffi-
culties regarding the origin of the dark lines in the
solar spectrum. In returning thanks, may I assure
him the evidence afforded by the phenomenon referred
to had been duly considered before I ventured to write
the letter on p. 114; but I arrived at the conclusion
that the want of chemical power in the light of the
solar prominences was the cause of some of the lines
changing from dark to bright.

He is, however, un

Query 3850.- Thermo" may perhaps unite the mer cury in his thermometer by giving it a series of sharp See also other correspondents' answers jerks. "Gitche Manito," some time since. Query 3875 ("Gratus ").-Bleaching powder is made by placing lime (moist) in a chamber, upon perforater. shelves, and submitting it to the action of chianice, evolved by the action of hydrochloric acid apone black oxide of manganese. Refer to corresponders answers on the subject in a recent volume.

MANUFACTURE OF OXYGEN (3883.-M. P. C. & Oxygen may be prepared from manganate of sods in heating it to a certain temperature in a retort whit connected with a steam boiler, and a pump whic The retort containing the manga lies air. first heated, and the tap from the steam boiler un on, when the following change takes place :(Na, Mn(s), + (H2O2 = (ÑaHO + Mn ̧0, +V, The oxygen being liberated, is passed on to the be When this part of the operation is over, the steam shut off, and superheated air pumped over the ture in the retort for about a quarter of an hour, whe it is again ready to undergo the first operation. Is air must be freed from carbonic acid by passing through caustic soda solution before being pang over the spent manganate. The manganate may be made in large quantities by heating to redness a mi ture of black oxide of manganese, carbonate nitrate of soda, the heat being continued for some time, in order to decompose the sodium nitrate, whe is at first formed.

Query 3887-THE UTILISATION OF SEWAGE.-S "On the Utilisation of Sewage by Irrigation and & tration," by C. E. Austin, Mem. Inst. C.E.; Belde Latham's "Inaugural Address," published by p and Baron Liebig's letter on the utilisation of t the subject to be found metropolitan sewage, published by Allnutt There plenty of information on scattered through the Engineer, Building News, and Gardener's Chronicle.

WATER ANALYSIS.-(" Aqua" 3886).—If “Aqua” is not accustomed to make analyses of different arti cles, and water more particularly, he should use Nicholson's process, which is admirably described in the Quarterly Journal of the Chemical Society for Decem ber, 1862. The apparatus required would be 2 burettes, 50 cbc., divided into 500 parte, with an Erdmann's float. The burettes must be provided with a glass stopcock in lieu of the indiarubber tube, and Mohr's clip; several small stoppered flasks, to hold about 100 cbc.; porcelain and glass evaporating basins, a few beakers, and a litre measuring flask. required are:-Standard lime solution: Dissolve 0172 grm. of selenite in a litre of water. Soap solution: The sapo mollis of the Pharmacopoeia is to be dissolved in a mixture of equal volumes of distilled water and methylated spirit, to be of such a strength that 22 divisions of the burette are required to produce a permanent lather with 50 cbc. of the standard lime solution. Barium nitrate solution: 026 grm. in a litre of distilled water.

Solutions

Silver nitrate solution: 85 grms.

I cannot agree with Mr. Proctor in considering
Kirchhoff right in ignoring crepuscular evidence. Nei-
ther, in my opinion, are the conditions wanting in the
upper atmosphere for the chemical combination with in a litre of water. Ammoniam oxalate, 0355 grm. in
a litre of distilled water. Chameleon solution: Dis-
Oxygen of iron, magnesium, &c.
doubtedly correct in considering that employing one's-solve 0-159 g:m. of potassium permanganate in a litre
self about photographic manipulations does not neces-
sarily teach anything concerning the nature of light.
That depends upon the character of the operator. He
may be an excellent photographer, although a poor
philosopher.
In dismissing this subject, I wish to add a few
words respecting the motive for its introduction. In
the hands of the astronomer the spectroscope has
proved of great service.
rologist it would be equally as useful. I hope this hint
will not be disregarded.

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His first

SIR,- As a rule, I do not care to call in question the
replies given in good faith by your correspondents,
but in your present number I find "Anti-Egyptian
gives a reply which is very likely, from its vagueness.
to mislead many of our fellow-readers.
remark, that it is useless to test a boiler unless the
plates and seams are visible, is quite correct; but after
that he states that a single rivetted boiler cannot be
worked at a higher pressure than 15lb. on the square
inch. Now, from old age or imperfect construction, it
may be that his engineer forbids him to work his own
boilers at a higher pressure, yet the statement that no
boiler can be worked beyond 151b. unless it is double
rivetted, is certainly a long way from the truth. I can
assure him that we have three Cornish boilers con-
stantly at work, from year's end to year's end, at a
pressure varying between 35lb. and 40lb.. and yet
they are all single rivetted.
ments be reconciled?

How can the two state

T. S. CONISBEE.

EXAM. QUESTION.
SIR,-"Zeta's" query (No. 3937) is very simple. The
weight of one litre of nitrous oxide at 0C. and 760
metre of mercury is 1-9712 grammes. 200 grammes,
then, must measure 101 461 litres, and as one litre
equals 61028 cubic inches, that is equivalent to a
volume of 6191 965 cubic inches. He can readily obtain
the weight in grammes of one litre of any gas at oC.
and 76 metres of mercury, by multiplying '0896 by the
atomic weight of the gas, and divide by its volume: as
for nitrous acids

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of water. These are the standard solutions required;
but for the analytical process I must refer Aqua" to
Nicholson's paper, the December part of the Journal of
the Chemical Society for 1862, as it would occupy too
much time and space to give it in detail.
VOLUME OF GAS (Query 3937).-" Zeta" can calen-
late the volume of gas thus:-11-16 litres of hydrogen
weigh 1 gramme; and as the density of nitrous oxide
is 22, that is half the molecular weight, 11:16 litres of
that gas measured at 0°C. and 760mm. would weigh 22
grammes. Now, as we know that 22 grammes occupy
Il-16 litres, we can easily find the volume occupied by
200 grammes :-

11.16 x 200

22

= 101 454 litres at 0°C. and 760mm. WEIGHT OF GAS (3956).-R. Terset can, by following the method here detailed, find the weight of any volume of gas. First, methyl gas is known by the formula (CH3 therefore, the density would be 15. {CH, Now, a litre of hydrogen at 0°C. and 760mm. weigh 0-0896 grm.; consequently, a litre of methyl would weigh 1344 grms. at the same temperature and pres sure. But the temperature is 20°C., whilst the pressure remains unaltered. A litre at 0°C. would become 10733 at 20°C. by the equation 1+ at or1+(0-003665 × 20). We can now easily get the weight of 1 litre, for we have found that 1.0733 litres of methyl at 20°C. weigh 1:344 grammes; what will a litre weigh? By the equation:-.

1344

1.0733

= 1.252 grms., or the weight of a litre of methyl gas 26°C. and 760mm. As regards the second part of the question, how to prepare acetic acid from the substances mentioned, he may prepare it thus: First slack the lime with water, and boil it with sodium carbonate to form sodium hydrate. This must be obtained in the solid state by evaporation.

NaCO3 + Ca(HO), = (NaHO) + CaCO3. The ethyl iodide is then acted upon by the caustic soda, and the resulting alcohol distilled off

CHI+NaHO = C2HO + NaI The alcohol' is then heated with sulphuric acid and potassium chromate, when aldehyde is formed:C2HCO +0 = C2H4 O + H2O and this aldehyde, when fused with caustic soda, forms the sodium salt of the acid, from which salt the acid is liberated by sulphuric acid:

CHO+NaHO = C2H2 NaO2 + H2 and (CH2NaO2)2 + H2SO4 = (C2H4O2)2 + Ñà2SO4 I hope I have made the process plain enough for R. Terset, and shall be most happy to help him on the road to knowledge whenever he chooses to ask. GEORGE E. DAVIS.

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