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judge by is the movement observable among the stars, and, as the stars are themselves in motion, it is not easy to separate the effects of their own motions from those due to the sun's.

Still, this problem has been attacked and fairly vanquished by astronomy. Il is true we cannot here get certainty, because we no longer have absolutely certain relations to deal with. But, as it is certain that, supposing the sun to be moving in a definite direction, there would result a balance of stellar motions in the contrary direction; we can obviously deduce the direction of the sun's motion, by noticing the direction towards which the stars show the most noteworthy balance of motion. This has been done, and in many ways. The result is that astronomers point confidently to the constellation Hercules and its neighbourhood, as including the point towards which the sun is speeding. His rate of motion has been estimated at about 150,000,000 miles per annum, or, between four and five miles per second.

I am only concerned here with the sun's proper motion, in so far as it relates to the earth's motions. The conception that the sun may be speeding through space with this enormous velocity seems, at first sight, so contrary to the fundamental hypotheses of modern astronomy, that many persons have been led to believe there is a real contradiction. They see that the earth's real path in space can no longer be looked upon as a closed curve, yet Kepler speaks of it as an ellipse; that, again, the earth, according to this new idea, is not travelling in a conic section, yet Newton says, all bodies under the influence of a central attracting force, such as gravity, must move in some conic section or other.

In reality, however, there is no difficulty. Modern astronomy only requires the earth and planets to move in ellipses with respect to the sun, not in space. Suppo-ing the sun at rest, and the planets moving in their present ellipses around him, and that then under the action of far distant suns, our sun began to travel through space, the planets would not (as Mr. Reddie fears), be left behind. They would be under the influence of those attractions as well as the sun. They would obey them then, precisely as he does, obeying all his influences as before. Thus their motions, with respect to him, would not be changed even by a hair's breadth.

CONCLUSION.

And here I draw these papers to an end. They have occupied much more space than I contem plated when I began, and yet each part of my subject has been dealt with far less completely than I could have desired. The fact is, a book, and no small one, is wanted to present at due length all the arguments which enforce upon astronomers the assurance that the Newtonian system is correct.

Would such a book be a desirable addition to modern astronomical literature?

I think not.

I believe that all sensible persons, even if, not capable of fully mastering the evidence in favour of modern astronomy, feel yet no doubts as to its truth. For them, then, such a book would be of little service.

For the paradoxists-dividing them into two well-marked parties, the knaves and the fools-what can be done? One cannot make the blind see, let one talk ever so fluently about light; and those who, having sight, refuse to see, are blinder than the blind, according to the true old proverb. Towards the paradoxists, then, of either order, one should act as Sir John Herschel is said to have done, when a rampant one told him he had squared the circle. "Indeed," said the greatest living astronomer, raising his hat, "then, sir, I must wish you good morning."

But while a set treatise, in defence of modern astronomy, would be a waste of labour, I believe, and hope, the matter I have just completed may have been of use to many readers of this journal. The greater proportion of them, those in fact for whom the ENGLISH MECH ANIC is specially int nded, have not time for a thorough investigation of the subject, yet possess the power of appreciating to its fullest extent the argumen's by which modern astronomy has been established. Knowing for whom I have written, I have not feared to be dry where my subject needed close and consecutive attention.

THE ROYAL POLYTECHNIC BARO-
METER.

membered in connection with some of the

inches in diameter. In the centre of this dial is the ordinary standard barometer scale, with its HE name of Admiral Fitzroy will ever be re-niers are set to the rise or fall of the mercury by two verniers for taking the readings. These verTH most important improvements in the science of means of a rack and pinion arrangement, worked meteorology generally, and in the barometer par- by the two keys seen just below the dial. So far, ticularly. The instrument which bears his name we have the ordinary arrangement for taking the is perfect as a weather indicator, and as such readings; but as this is not always clearly under stood, Messrs. Davis have supplemented it by placing on the right side of the dial two columns of remarks which refer to changes in the weather, one column showing the winter, and the other column, the summer changes. On the left hand of the dial these two columns are repeated, and are intended to record the weather of the previous day. The indications are effected by a simple and ingenious arrangement in connection with the verniers. On looking at the engraving, it will be seen that there are two hands or pointers radiating from the centre of the dial. These pointers are centred loosely on a pin fixed behind the tube, and each passes through a slot cut in the verniers, which thus hold them up. Now when the verniers are raised or depressed, the hands must follow the same direction; and according as the verniers are placed at the height of the mercury, so the pointers stop opposite to a statement of the weather that height indicates. The right-hand pointer is set to show the weather expected to-day, whilst the left-hand is set to record the state of the weather yesterday. The mechanism of the instrument is exceedingly simple, and is not liable to get out of order.

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has had a prize medal awarded to it, and is known
as Admiral Fitzroy's prize medal barometer. But
although perfect in itself as an indicator, and
although clearly comprehended by those who are
accustomed to the reading of such instruments,
experience shows that to make it universally use-
ful, its readings must be rendered in clear and
definite language. Its price is within reach of
all, and it only wants to be made intelligible to
the most ordinary observer. To meet this re-
quirement, Messrs. Davis & Co. have improved
the apparatus in the manner shown in our en-
graving. Their Fitzroy barometer forms the
base of the new instrument; this consists of the
mercury tube with the cistern in one piece, which
is enclosed in an oak case. On the lower part of
the case is a thermometer, and opposite to this
are diagrams of Admiral Fit:roy's storm warning
siguals. These are surmounted by tables ex-
plaining their meaning. The novelty is in the
upper portion of the barom ter, which will be
seen to terminate in a circular dial about 10

PROCEEDINGS OF THE ROYAL
ASTRONOMICAL SOCIETY.-MAR. 11, 1870.
W. LASSELL, ESQ., F.R.S. IN THE CHAIR.
(SPECIAL REPORT.)

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had been read and coufirmed, the first paper communicated was from W. Marth, Esq., containing observations of position angles, and apparent distances of the Satellites of Uranus from the primary, which was ordered to be printed forthwith. Lieutenant Herschel communicated, through his brother, a paper remarking on a curious appearance, as seen on the Sun's disc. The author remarked that in October last, while preparing to observe the prominences of the Sun with a spectroscope, an unusual phenomenon presented itself, consisting, apparently, of a train of dark shadows and light streaks on the solar disc, which were at first thought to be sparks in the tube of the telescope, but the permanence of the phenomena did not permit of this explanation. The possibility of this extraordinary appearance being occasioned by the transit of a system of meteors, next occurred to the observer, and preparations were made to observe the circumstances of the transit with all the care possible. The image of the disc of the Sun was thrown on a screen, and the equatoreal telescope set in motion. The apparent size of the shadows was shown on the screen, and they were observed all that day. On looking at the Sun the next day, the same pheno. menon was observed; the objects were still seen passing in a continuous stream. The direction was 150° E. by N., or perhaps two streams not very far distant. The dark objects. were out of focus when the Sun was in focus, and were cloud, and notwithstanding the Sun's light they still seen when the Sun was partly obscured by were seen after they left the disc; and the smaller they were, the less was their velocity. The direction of motion of one only was retrograde; and one entered slowly, and then changed its direction. Every care was taken to notice every pec uliarity presented, till the observer convinced himse If that he was watching the motion of a number of locusts, passing in continuous succession between the instrument and the Sun, and however curious the phenomenon might be in natural history, it was clearly not of an astronomical character. The author endeavoured to account for some of the peculiarities seen in America at the time of the Eclipse last year, by referring them to the same cause.

Mr. STONE remarked on the necessity of a change of focus, in attempting to explain any peculiarity of this nature, which was the best means of effectually settling the question.

Captain NOBLE remarked that in a previous number of the "Notices," would be found the re

10

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marks of Mr. Reed, on a similar question, whose question. Mr. Stone hoped that the observers
suggestions led Mr. Dawes to focus for the well-would not confine their observations to any par-
known thistle seed."
ticular locality in the Corona, but examine all
positions of it.

Captain NOBLE communicated three short papers to the Society. One on occultations of Stars by the Moon; an observation of Venus, near her inferior conjunction; and an observation of the Zodiacal Light. In the second paper Capt. Noble said that the state of the sky prevented him seeing the planet till about two hours after her conjunction, when he saw a very narrow thread of light, not quite semi-circular, and saw the body of the planet projected on the sky beyond, sensibly darker than the surrounding sky. On the 3rd March, 7h. 40m., the author saw the most brilliant exhibition of the Zodiacal Light that he ever witnessed in this country. Besides its brilliancy, two peculiarities were noticed, namely. that it was very nearly perpendicular to the horizon, and the axis inclined to the ecliptic at an angle of 20o.

Mr. BROWNING exhibited some drawings of Jupiter, and remarked upon the many changes of forin and colour of the belts of Jupiter, the principal of which seems to have been a sensible widening of the Equatoreal belt to nearly double its former dimensions. Mr. Browning invited the attention of observers to a consideration of the Planet, which the peculiarities it presented rendered interesting at this moment.

The PRESIDENT seemed to suspect some slight exaggeration of the colour and outline of the Equatoreal belt, bat Mr. Browning defended his drawings, which appear to have been carefully made.

MODERN CHEMICAL NOTATION.
BY DR. FERD. HURTER,
(Concluded.)

2

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The sbove formulæ are sufficient to show us the use of the chemical alphabet.

The first of these formulæ as well as the second and third symbol which is intended to convey an idea of the manner in need no comment. Potassic sulphate is represented by a

WHEN the atomicity or basicity of the element should be expressed by the symbol, then the letter is provided with another figure at the top, but this figure must be a Latin one. The sign 011 means accordingly that one atom oxygen possessss two equivalents, or better, that one atom of of oxygen can combine with two atoms of a monogenous element. This latter way of expression is the more general one. which the single atoms are connected. The sulphur being tetravalent is connected with two atoms of oxygen, which are When a number of atoms of the same element form one (if the compound must be saturated) again combined among group, then the Latin number at the top is the expression for themselves. Thus the group SO, has still two equivalents of the capacity of saturation of that group, or, as it is also sulphur left free to attract other atoms, which we find to be termed, for the atomicity of the group, or still otherwise, for oxygen atoms, each combined with an atom of potassium. the quantivalence of that group of atoms. In this way we The same formula would apply to hydro-potassic sulphate in write 0,11 or Mn,VI, and understand by it, that 5 atoms of one atom of potassium is replaced by one atom of sodium. The oxygen can combine with only 2 atoms of a monogenous group SO, we find in formula (7) representing alum to occur element, that 2 atoms of manganium can combine with 64 times. Alum is a sulphate like hydropotassic sulphate. atoms of a monogenous element.

The same rules apply to groups of atoms of different elements-for example, COir indicates that one atom of carbon is combined with one atom of oxygen, and that this group is able to combine with two atoms of a monogenous elemeat. When, however, a formula should be quite a rational one and express the function of each equivalent of the various elements forming the compound, then the letters and figures are not always sufficient, and we have to enrich the chemical alphabet with a few more signs. Instead of using a Roman figure at the head of the letter to indicate how many atoms

Each SO, is connected by 2 atoms of oxygen on the one side
to the aluminium, on the other to either hydrogen or potas-
sium. The metal aluminium has, like all metals of the
same group, the property of occurring as a group of two
atoms, which by their combination saturates 2 of the 8
equivalents of which they naturally consist. The two alumi-
nium atoms are directly united with one atom of oxygen,
saturating two more equivalents of aluminium, so that at
replaces four atoms of hydrogen in four molecules of sul-
last we have the group A10 being tetravalent. This group
phuric acid, forming the compound
ALOH
4 502

of a monogenous element the element represented may com-In
bine with, horizontal or radiating strokes are used, as many
in number as the Latin figure indicates. Thus one often finds
0 instead of Ou, or

I

0" or

= instead of c

Some chemists use still more symbols. They represent all the monogenous atoms by a circle, and all the other elements by combination of as many circles as the element's quantivalence requires. Such signs are represented by the following:

Or

о

The last paper was from Mr. Proctor, having reference to the Corona seen in total eclipses of the Sun. Mr. Proctor said that at the next eclipse of the Sun, which occurs next December, in Spain, the attention of astronomers would be drawn to the Corona with a view of explaining the difficulties that it now presents. The author of the paper contended that the phenomenon witnessed could not be owing to terrestrial causes, for in cases of total eclipse the Moon is seen projected on the corona, which could not be if the light was occasioned by the Earth's atmosphere. He added that in an annular eclipse, the centre of the Moon has been seen darker than the edge; and that in partial eclipses the edge of the disc has been seen projected (dark) on the background of the sky, as often as the observer has looked for this particular, which would Monovalent. Divalent. seem to disprove the existence of an atmospheric glare. Mr. Proctor argued from Captain Noble's remark concerning the visibility of the dark part of Venus when in the neighbourhood of the Sun, the existence of a continual brilliancy which might be owing to the richer part of the Zodiacal Light, which increases in brilliancy as it approaches the Sun, and in the close neighbourhood of the Sun itself doubtless merges into the Corona. In concluding his remarks, the author conjectured that the Zodiacal Light itself was the collection of the richer portion of the meteoric streams, perhaps incandescent, where near to the Sun. He remarked that numerous meteor streams must exist, since the Earth meets with 56 of these systems, and that if the Great Comet of 1863 was followed by a train of meteors similar to that that accompanies Tempel's, the near approach of these to the Sun must produce an effect which can easily be supposed to resemble that witnessed where the Corona is brightest. Mr. Proctor hopes that the Society will form a committee to consider the best mea is of setting at rest the vexed question of the Corona, and made some suggestions which he thinks likely to produce that end.

It was asked at the meeting if the Government were proposing to render any assistance to astronomers that intended to go to Spain to view the Eclipse of the Sun next December?

The PRESIDENT replied that the Government certainly had not proposed any such measure, and were not likely to, but that the Council were now discussing the mode of application to Government, and the best way to derive results that were likely to follow from the observation.

Mr. STONE observed that he hoped that three observers might make observations on the polarised light, as two would probably differ in their results, and the observations of the third would be needed to settle the question. If anything had appeared to be settled by the Indian Eclipse, it was the question of the polarised light, which the observers agreed to have been polarised in a plane passing through the centre of the Sun, but the American observations had again opened the

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H

which finally two atoms of potassium become substituted for two of the hydrogen atoms. The sign is a remainder of the theory of types; it now is used to indicate that the two parts which it connects are held together by the elements it points to. O mean that the two atoms of hydrogen are held together by one atom of oxygen. In organic chemistry this modern notation is invaluable. Inorganic chemistry, however, can be taught just as well by means of the old notation. Still the former has its peculiar advantages, and will no doubt help to further chemistry, where the constitution of bodies is so well studied the knowledge in that department as it has done in organic that we can deduct almost every property from the formula. We can, with a certain degree of accuracy predict the properties of a substance from its formula in inorganic chemistry, but not to the same extent as it is possible in organic chemistry. Here we derive from the formula the specific gravity of a liquor at boiling point, the boiling point itself. A well written formula tells us how many hydrogen atoms can be exchanged for a metallic atom, or for acid radicals. tells us at once whether the substance has more the properties of an alcohol, or of an acid, or of a base. It tells us, as we have discussed in our last paper, the specific gravity of the gaseous state and the quantity of heat necessary to raise the substance's temperature one degree.

It

It is evident that the chemical formula will not be perfect until it represents all the properties of matter as it does now a few. And when chemistry will make as rapid progress in the next twenty years as it has done in the last twenty we shall soon arrive at that perfection of our knowledge which Berthoilet thought to have arrived at some 70 years ago when he

However, the letters, and, if necessary, the horizontal
strokes, are quite sufficient to make the rational formula of a
substance perfectly clear. It is, as a chemist of high standing
said, perfectly useless to attempt to give any other represen-published his Essai de Statique Chimique."
tative to the atom than its letter. Any drawing cannot but
lead to too mechanical a view of the constitution, and we see
in the present periodicals plenty of proof of the nonsense
which such mechanical views, when used to too great an
extent, will bring forth.

As the whole system of notation will become clearer by
citing a few examples and discussing them, we append here
an assortment of modern formulas and some explanatory notes
as the conclusion of this paper.

(1.) Water

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(2.) Potassic K
hydrate. H

(3.) Potassic K
chloride. CI)

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0 = [0]= KHO

= KCI

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но

= KOHO

= KCl

Hoping that I may have helped some of the readers of the ENGLISH MECHANIC to an understanding of the leading principles of the modern theory, I conclude my paper, asking the reader's indulgence for my want of style. I feel that have not the English language sufficiently at command to expose my ideas always so clear as I should like to have done.

EMIGRATION.-Professor Goldwin Smith writes to a friend in England a letter on emigration as a means of escaping the economical difficulties and perils which he fears are gathering round England. Elder formula. The professor commends the Southern States of America, especially Virginia, as better worth the attention of emigrating Englishmen than either Canada or the Northern States. He says, the Southern States are more English than any other portion of America, and that Englishmen in those States would find both a generous welcome and an ample field for their enterprise,neither of which are to be so readily found in the Northern States, where Englishmen do not and cannot iraternise with the Irish, German, or native American population. "In the Northern States" says Mr. Smith, "the English emigrant now finds himself, I am sorry to say, not only in a foreign but a hostile country. And as a practical and likely means of securing a solid home in Virginia, he mentions that there is a Virginian Land Company in New York, presided over by General Imboden, one of the Confederate Commanders-that he has had communica tion with the company and seen its papers, and that we are likely to hear of its movements in England. It should be added that he intimates that English predelections for Canada are a mistake, both on the grounds of climate and other natural and agricultural difficulties in comparison with Virginia and other Southern States.

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LETTERS TO THE EDITOR.

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

All communications should be addressed to the EDITOR of the ENGLISH MECHANIC, 31, Tavistockstreet, Covent Garden, W.C.

not letting it sink to the bottom of the vessel; place
the vessel containing the above in a sand bath, and
submit it to a temperature of about 90° C. (194° F.).
Then take a retort furnished with a leading tube,
which dips into the vessel in the sand-bath; place in
the retort 540 parts of manganese dioxide (Mn.O),
cover with hydrochloric acid, and apply heat Chlo
rine will be liberated, and pass over into the solution
containing the baryta, which latter will be decom-
posed. Barium chlorate and barium chloride will be
formed, and will co-exist in the solution together.
The chlorine must be passed in until the milkiness has
disappeared. More
dioxide may
manganese
be
required than is stated if the sample be very impure;
but if 600 parts are taken, that will generally be found
sufficient. The reaction which takes place may be

All eheques and Post Office Orders to be made pay- thus represented :able to J. PASSMORE EDWARDS.

I would have every one write what he knows, and as much as he knows, but no more; and that not in this only, but in all other subjects: For such a person may have some particular knowledge and experience of the nature of such a person or such a fountain, that, as to other things, knows no more than what everybody 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.

CONES FLOUR.-BARIUM CHLORATE-TEST

FOR ARSENIC.-SODA CRYSTALS, &c. SIR,-On page 633 of your valuable journal a correspondent, siguing himself "One of the Old School," has expressed an opinion that my statement relative to the adulteration of cones flour with rice is incorrect. Now, we are aware that revet wheat is the proper wheat to use for the manufacture of cones flour; but I say that rice flour is wholly and partially substituted for that article, according as the price is intended to be high or low. Some bakers at Eton pay 36s. to 41s. per sack for good flour, and for cones from 20s. to 25s. I do not mean to say that 20s. is the regular price, because of course that varies; this flour, cones for dusting, as supplied at the present time here from 238. to 258., consists of nothing else but rice flour; and on applying to various bakers in the neighbourhood for a sample of cones, I invariably obtained pure rice flour. On one occasion I inquired minutely into the sale of this cones, and I found (a rice flour variety) that it was labelled "cones," invoiced "cones," and inserted in the account as cones. The bakers about here, as I have said before, pay 36s. to 418.; and if they pay (now) 23s. to 25s. for cones, it is hardly likely that it can be pure wheat flour. Once, and once only, I obtained information to the effect that nearly the same price was paid for cones as for flour; and when it was found that there existed a cheaper variety, 268.,

it was obtained directly.

After having expressed my opinion on the matter from direct observation, I will take "One of the Old School" to a work called "Adulteration Detected in Food and Medicine," by Dr. Hassall, page 277.

Dr. Hassall says: "Dr. Paley, of Peterborough, brought a sample of flour seized on suspicion, and which the baker called 'cones flour. On subjecting this to microscopical examination, it was found that it consisted entirely of rice flour."

(BaH2O26+ Cl12 = (BaCl2)5 + Ba (C1O3)2 + (H2O6 The action of the chlorine being continued for a short time after the milkiness has disappeared, the clear liquid (if necessary) may be filtered, and the filtrate evaporated to dryness. 2000 parts of water are then added to the residue, the whole raised to the temperature of 10 C., and set aside to cool; the barium chloride will remain in solution, and the chlorate crystallising out. 316 parts of this latter salt would be formed by taking the above quantities.

STRAINS ON GIRDERS.

W

SIR, Will you kindly allow me to make a few remarks in connexion with J. W. Bedford's notes on "Strains on Girders" which appeared in your last impression? The action of a load placed at the centre of a girder is as follows:-Let A B represent a girder 20ft. span, 2ft. deep and W = 10 tons. is supported at A, and the reaction at A saused by the bent lever ACD is increased 5 times in compressing D. There fore, strain at centre = 55 25 tons.

W

2

10
2

2

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W load, equally distributed. 7, length in terms of
depth, s, strain of compression at top flange, or
Wxl
tension at bottom flange. S =
Now, 10 tons
8
placed upon the centre of the girder in question will
be equivalent to 20 tons equally distributed. Hence,
the formula becomes

20 x 10

8

= 25 tons strain at centre.

HYDROFLUOSILICIC ACID.-"Taffy," although pro-
fessing to correct me in the barium chlorate prepara-
tion, has failen into an error himself with regard to
the above acid. "Pyro" can prepare it thus:-Take
one part each of finely-powdered fluor spar and pow-
dered glass, or fine sand, and mix with 6 parts of con-
centrated sulphuric acid (H2 SO1). On applying heat
to the mixture, gaseous, silicon tetra-fluoride is formed:
(H2SO4)2 + (CaF2'2 + SiO, = (CaSO1), + SiF +(H2O)1⁄2
A precipitating glass is then taken and partly filled
with distilled water. Some mercury is then placed in
the bottom, and the tube delivering the silicon tetra-
fluoride is made to dip into the mercury; the gas as it
passes out of the mercury is decomposed by the water,
forming gelatinous silica and hydrofluosilic acid.
This latter is not "a gelatinous mass," as "Taffy"
states; the silica may be separated by filtration
through a cloth, while the clear liquid is hydrofluosilicic
acid (H,SiF). This acid, when concentrated, fumes
strongly in the air; when added to potassium chlo-
rate, an insoluble potassilicon tetrafluoride is formed, bottom flange area of 6in., then
liberating chloric acid. This chloric acid solution
may be poured off the insoluble precipitate and neu-
tralised with barium carbonate, and followed out as
Taffy "states. The following reaction takes place
on passing SiF, into water:-

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(SiF4)3 + (H2O)1⁄2 = SiO2 + (H2 S! F61⁄2
PURIFICATION OF CHLORIDE OF SILVER." W. H."

will find that heat is the proper method for separating
paper from his silver chloride. If he dissolves the
chloride by means of ammonia, he must recover it by
spontaneous evaporation. If he attempts to drive off
the water by the application of heat, he will find that
fulminating silver will be deposited. I merely men-
tion this because I find "Ernest" and "Beta" had
both forgotten to mention it, and "W. H." instead of
recovering his chloride, might lose his head. The
excess of ammonia might be neutralised by the addi-
tion of an acid before evaporation.

TEST FOR ARSENIC.-Let "Claudius" proceed thus:-Procure some pure zinc. free from arsenic, and place it in Marsh's apparatus with the substance to he Page 279: "It appears therefore that cones flour is tested. Add sulphuric acid, and when the gas is rarely to be obtained genuine, but is subject to an enor being given off freely light it, and hold a crucible lid mons amount of adulteration; further, that some of the in the flame; if arsenic or antimony are present, there samples do not contain a particle of wheat flour, of will be a metallic deposit upon the lid. To discrimiwhich alone they should consist." nate between antimony and arsenic, the metallic depoTwenty-two samples of "cones flour" were pro-sit must be submitted to the action of a drop or two of cured chiefly in the metropolis: the following is the yellow sulphide of ammonium; antimony dissolves, and result (this is also taken from Hasall's work). At the arsenic remains unaltered. To test the cleanliness of same time, I think it is a mistake to say that bean the apparatus, use the zinc and sulphuric acid alone. four is found in cones. The samples below, in which If clean (free from arsenic) and the materials pure, that article was found, were in all probability infe- there ought to be no deposit upon the lid. Arsenic rior, adulterated varieties of wheat flour :may also be detected when in solution by giving a green precipitate with cuprammonium sulphate. The precipitate consists of arsenite of copper.

1. Contains rye and rice flours. 2. Entirely rice flour. 3. Contains rice flour. 4. Contains rice flour. 5. Consists in great part of rice flour. 6. Genuine. 7. Almost entirely rice flour. 8. The same. 9. Chiefly rice and bean flours. 10. Contains much rice flour. 11. Not cones at all, but consists of rice, Indian corn, and bean flours. 12. Bean and rice flours. 13. Contains much rice flour. 14. Contains barley flour and alum. 15. Genuine. 16. Barley and rice flour. 17. Consisting in great part rice flour. 18, 19, and 20 were genuine. 21. Not cones at all, consisting entirely of rice and Indian corn flours. 22. Consisting chiefly of rice, with some

POWDERING PHOSPHORUS.-" M. P. S." can reduce phosphorus to an impalpable powder by dissolving it in bisulphide of carbon, and letting the latter spontaneously evaporate. By-the-bye, I may as well add that the latter operation is best performed in the open air, if the operator is blessed with the sense of smelling.

The breaking weight of this girder may be found
by the following method:-Let a sectional area of
bottom flange in inches, d = depth in inches, and s =
span in inches. 744 tous a constant for wrought iron
ax d x 74-4
--= breaking weight in
girder or tube.

tons at centre.

44.64 tons.

8

Let the girder in question have a
6 x 24 x 74.4

=

240 ROBERT PICKWELL.

QUESTION FOR MILLERS.
SIR,-In answer to "C. J.'s" personal question, I
beg to say I have only in one instance had the trouble
he complains of with the neck of the stone spindle,
which happened some time since in a mill I was
carrying on off-hand, when I had to take the stones in
hand myself, and flayed two high sides of the bed-
stone, and when I had dressed them two or three
times myself the neck went all right, and has been no
further trouble the last two or three years. I will
also add that I rectified the running balance at the
same time.

To the second question, I never yet saw a thick top
heavy stone running satisfactorily on a short spindle
and I have always kept the greater part of the weight
of the stone below the bearing in my own mills, and
shall continue to do so. Some years since one pair
were fitted with universal iron, like the ship's
compass, with the bearing near the face of the stone;
but they had to be removed and replaced by cross bar
and driver.
R. R. SMITH

REFLECTORS AND REFRACTORS.
STR,-It is nearly eight months since I last wrote to
you on the above subject, and I then promised your
readers, should they so desire it, to supply them at
some future time, with a further description of the
84in. mirror and its performance. From the kind
allusions which some of your correspondents have
made to this promise of mine, and to the matter con-
tained in my former letter, and from the increasing
interest with which, I am glad to say, the subject of
practical astronomy is every week being invested in
your columns, I feel I cannot do better, during a period
of enforced rest from professional labour, than state
what I have found that performance to be, and drop
some further hints to amateurs, who, like myself, are
anxious to render their home-made telescopes as per-
fect and useful as possible. I had thought of giving
a brief résume (with the Editor's kind permission) of
the work done during the past half-year, but found it
would occupy far too much space and trespass too
much on your indulgence, to think of such a thing, so
I shall simply state the work done on one or two
favourable nights last summer, and leave the reader to
form his own opinion of what the telescope has since
accomplished on similar nights.

SODA CRYSTALS.-In the manufacture of soda crystals, the first step is to form a sulphate of soda. This is done by placing a quantity of common salt in a Indian corn flour and much salt. decomposing pan, and running in an equal quantity of Now, the preface to the above work is dated 1857, oil of vitriol. When heat is applied, hydrochloric and "One of the Old School" will perceive he is acid is given off, and may be condensed in towers or decidedly behind time when he finds that Dr. Hassall scrubbers. The mass is then raked out upou the found in cones flour that which I stated I found, in my hearth or roaster adjoining the decomposing pans, letter on starch. I am glad to find he can "conscien- and submitted to a somewhat higher temperature. A short time after I had written the former letter. tiously affirm that no rice, beans, or any other inter-The salt-cake thus produced is mixed with an equal describing the mounting of the Shin, mirror, which I mixture ever entered a sack of his." He says that quantity of limestone and two-thirds its weight of had obtained from Mr. Browning, of the Minories, in some of the "new school" add dry bean or white pea coal. A charge of this mixture is introduced into a the end of June or beginning of July, we, in this flour to wheat flour, to give it strength, but that cones reverberating furnace, heat applied, and when com- neighbourhood, were favoured with four nights in should consist principally of rice, and yet sold and pletely fused it is raked out into moulds. This product succession of most exquisite definition, a boon indeed accepted as cones flour is a novelty." We (all of us, I is called black ash. This product is digested with to those who possessed really good instruments, which may say) read the ENGLISH MECHANIC for two pur- warm water, the clear solution evaporated to dryness poses-first, diversion, the principal motive, aud and heated with sawdust, to convert any caustic soda they wished to test. On the first of those occasions, in the early evening, just as the sun was setting, I instruction the second. "One of the Old School' into the carbonate. The residue is then dissolved in brought out the large telescope, and having inserted a then must own that he has not subscribed for naught; hot water, decanted off from any insoluble matter, large field eye-piece, giving a power of 35, and a field he has gained a wrinkle, and that is, that rice flour is and run while hot into crystallizing pans. After the of 3 degrees, directed the telescope to the position in sold as cones, labelled and sent by rail as cones, paid first crop of crystals have separated, the mother liquor the sky where the planet Saturn would probably be for, aye, and the purchaser satisfied by paying rice is drained off, and evaporated for a second crop. Does found. After some little searching, I successfully flour price for CONES. Hassall says that there are "Soda Crystals" infer that his decomposing paus several kinds of cones in the market, the best being hold 120 gallons, or that that is the capacity of his picked him up, shining with a pale silvery light, in s nearly twice the price of the worst, the adulteration crystallizing paus? If the latter, they would hold sky which appeared, with that power, of a deep violet line. Viewed under such circumstances with a large being usually in proportion to the price." I can tell. 60wt. of soda crystals, deposited from solution. By directly I see a loaf, which kind of cones the baker a little calculation he will be able to arrange quanti-telescope, and with the evening light still bright, the planets present a most beautiful appearance, one uses, real cones or rice flour. tities in the proportions given above that will suit his which often tempts the observer to neglect for a time plant. the use of higher powers, but of course, if the physical details of celestial objects are to be investigated, they must be used.

BARIUM CHLORATE.-As there seems some difficulty in "Pyro" getting an answer to his query relative to the manufae ure of barium chlorate, I will furnish him with the various minutie:-Take 918 parts of barium oxide (baryta), finely levigated, and suspend it, in water, keeping it in a state of suspension-i.e

"Practical Chemist" (Query 2054) is easily answered. There exists no acid termed "hypochloric" acid. flypochlorous acid is known, having the following molecular formula, HCIO.

GEORGE E. DAVIS.

The definition I knew to be most excellent, for, with a little experience, one look at the circle of light which is formed in the eye-piece, when a bright object

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is slightly out of focus, will tell this, if the illuminated erele is steady and calm, without any bubbling or waving motion, after the telescope has been for some tom to the air, the observer may prepare for good work This steadiness, too, is not in the least affected by the beautiful pulsations of coloured light which cer from the larger stars, but refers equally to them. It was peculiarly so on this ocession, for having inserted, first a power of 100, and then, as the evening darkened, 187, I was enchanted and completely chained to the spot with the exquisite appearance of the planet Saturn, without one trace of haziness or of indistinctness of outline; it seemed chiselled out in colours of purest silver and pale sky blue, and golden yellow. The dark division in the ring was sharply marked all round, without a break in its continuity, spreading out into a dark band at the "anse," and narrowing at the minor chord of the ellipse into an infinitely fine black line. The transparent ring too was so evidently and beautifully seen, of a dusky grey colour, and clearly less bright on the side next to the rings, than on that next the planet. This I took particular note of, and examined it most carefully on the two following evenings, when it was verified beyond all doubt. It is not noted in the engraving of this planet in the interesting little work by Mr. Lockyer, copied from Mr. De La Rue's sketch, but is very well marked in the lithograph on the frontispiece of Mr. Browning's pamphlet. On the occasion above mentioned, it was plainly seen, not by myself alone, but by two other gentlemen, who were examining the planet with me. We also directed our attention to the outer ring, and searched with the greatest care for some trace of a division, but could not detect any line which might be rightly so called; there was a shading sometimes visible, more guessed however than clearly seen, which might possibly suggest the idea, but did not satisfy me. During the time I was observing the shading on the transparent ring, and searching for a division on the outer one, five of the enterites had come into view. On the second evening I saw the sixth, and had glimpses of the seventh if it was not a very minute star, for not having any ephemerides of the satellites, I could not absolutely identify it), with the six satellites however, so clearly seen, and the body and rings of the planets so beautifully defined, your reader will believe me when I say, I never saw a more wonderful or more fascinating object.

There was one thing about this strange planet which delighted me, even more than all I have yet described. I refer to the colours on the ball and on the rings-it is only on such nights as these I am speaking of, that this phenomenon can be seen to any advantage, and to see it well a large aperture is absolutely necessary. I do not know how most astronomers account for these colours, whether they think them intrinsically inherent in the planet or its atmosphere, or to some extent caused by the vapours in our own atmosphere, through which the light of the planet has to penetrate, certain it is that they are much better seen and brighter, when the planet is near the horizou, provided only high powers can be used, than when it is more overhead. I believe, too, the larger the aperture the more clearly are they marked, so that the possessors of large telescopes have a very great advantage in this respect, over those who are not so fortunate. On the night in most admirably in my reflector of Shin. I could well question, I found that a power of 350 showed them imagine, however, the much greater brightness and beauty they would have in a 121n, or 15in, speculum. The contrast between the delicate sky blue of the poles of the planet, the golden yellow, alternating with silver and grey on the belts, and the blending of all these hues on the rings, was indeed a lovely sight, but should be looked for and seen to be at all appreciated. The beautiful appearance which Saturn presented on that occasion, lingers in my mind still, and although I have seen the globe of Jupiter under equally favourable circumstances, with far more marked and darker hues on his belts and brighter tints altogether, the soft delicate beauty of the planet Saturn surpasses in perfection and loveliness all else I have ever seen in the infinite amplitude of space. I have dwelt thus minutely on these observations of Saturn, because they have made a lasting impression on my mind, and showed me what a perfect speculum will accomplish under favourable circumstances. But to continue my description from my note of these evenings.

The planet Saturn is setting, and at last drops behind the roof of a neighbouring house, so I am reluctantly compelled to turn the telescope to other objects, and surely here are a great variety of most interesting double stars, some of them excellent tests, and all very favourably situated for observation. Here is Aquilæ, à Ophiuchi, 7 Ophiuchi, 7 Cor. Bor., & Cygni, u Boötis, all just as well placed as they could be. Here are also two remarkable nebulæ, M

the components of this star are only 0:55 apart, and
it was with fear and trembling I approached it on the
first night, but what was my joy and delight, when I
had applied a power of 300, to see the discs clearly
separated by a black division, yet looking square!
When, however, I had applied a power of 350, the
division was perfect. Again and again I looked at
this beautiful object, two 8 magnitude stars, like most
minute circles of light, lying so exquisitely close to
one another yet perfectly distinct. I thought I
detected a slight difference of colour in the com-
ponents, and hope, when the calm summer weather
comes again, to make many more observations on this
star, for a most wonderful and interesting object it
certainly.
While speaking of this star I may mention, that it
scems somewhat more easy to divide than y Andro-
meda, which I have nicely separated on some favour-
able occasions since; perhaps this may arise from the
greater magnitude of the latter. I will finish what I
have to say on the subject next week.

H.

RECENT QUERIES AND REPLIES FROM
MILLERS.

shoddy manufacture. Tat used for opening raw cotton is called the willow, which name he makes use of, but that used in the shoddy manufacture is called the willey. Now, the willowing or scutching machine, is composed of a feeding apron and two sets of rollers and beaters. The first set of rollers, turning in opposite directions, drag the raw cotton through, and transfer it to the first pair of beaters, which, revolving with great rapidity, thrash out nearly all the sand and other impurities which the wool contains; the second pair of rollers and beaters complete the process.

It will thus be seen that" Scrutator" has jumbled together the two machines, owing to the similiarity of the names; "rushed headlong into print," to use his own expression, without taking taking the trouble to investigate and thoroughly "master the subject; has drawn hasty conclusions, and tried to criticise what he apparently knows nothing about. GITCHE MANITO.

METEOROLOGICAL.

SIR,-Would you, or some one of your readers, give information how to observe the daily changes going on in the horizontal and vertical motion of the needle, as well as the intensity of the magnetic force?

Is there not some more simple way of observing and recording these variations and earth-storms, than the complex apparatus in use at some observatories?

J. W. A.

THE ILLUMINATED PORTION OF THE MOON.

SIR, Mr. J. Sharpe, in answer to several correspon-
dents, denying that I am the inventor of the universal
joint, described on page 526, No. 255, says that he has
had the same working in his mill since 1856, while the
description he gives of it seems to represent quite
another thing. Perhaps Mr. Sharpe will be kind
enough to send a drawing to your excellent engraver
of what he means by the following sentence: The
oval ring of mine has the journals at the foci of the
transverse dia., which admits of the inner ring, or
SIR,-When I called your attention to an apparently
driver, being shorter, and therefore stronger, and anomalous appearance in the illuminated part of the
leaves more room between them "-without which the moon, it was with the view of affording or eliciting
following sentence seems quite incomprehensible- information for the more observant of your readers.
viz., that the centres of all his journals are in the
on a subject which probably has puzzled many of
same circle, which could not be so in mine. I main-them, but I had no idea of its being so followed up or
tain that the centres of my invention are in a circle; for so long a time. When the letter of "Sigma" ap-
therefore, if bis joint is anything offferent to this, as peared, I thought his sati-factory explanation would
he says, all his centres cannot be within one and the have been generally accepted, and though I think his
same circle. My object in forming the oval ring was diagrams might have been improved, I forbore to
to bring all the centres within a circle, so as to cause trespass more on your space, or to tax your engraver
the stone to oscillate alike on all the four bearings. further. But as Mr. Beardsley cannot accept the
The centres are also in the same plane or level. It is explanation of "Signa" and has sent you a diagram,
therefore a perfect universal joint in every respect, and I cannot help writing a few words on the subject,
as it stands is purely and simply my own invention. especially as his diagram is pretty nearly what I would
I also repent my former assertion that it is superior have sent myself, and helps to prove "Sigma's "
(until convinced to the contrary) to anything at pre- views instead of his own. If any of your readers
sent in use. May I invite Mr. Sharpe to send to the will place a pin to represent the position of an ob-
MECHANIC the first new thing, as he deplores so much
server on the earth's surface where Mr. Beardsley
the antiquity of all hitherto sunt respecting milling?
supposes him to be, another lin. above it to represent
the centre of the moon, and a third at a distance of
33ft. in the direction of Mr. Beardsley's retiring suns,
and to do duty for one of them, the relative positions
of the three bodies will be nearly obtained; a thread
SIR.-Without any wish to find fault with other then passed round all will show how very nearly
suggestions, I send you a description of a band of parallel the rays of light from the sun to the earth and
simple and cheap construction, and of the efficiency moon are, and thus prove the contrary to what Mr.
of the action of which I have had several practical ma's" explanation. The enlightened part of the moon
Beardsley puts forth as his argument against Sig-
proofs. A strip of copper and one of zinc, of any is directly opposite the sun, although the latter
desirable length, are to be joined (by rivet or any other
together by thread, and varnished with shellac in by Mr. Beardsley.
preferable mode), at the ends, the joint whipped appears on the tangent to the earth's surface shown
alcohol; the extreme ends having a hole punched in
each, for fastening with a silk ribbon, or ether non-considered an authority with that gentlemen; he pro-
conductor. To apply and bring the same into action, bably will be by most of your readers, and I therefore
wind a piece of list spirally round the united strips of beg to quote from his "Outlines of Astronomy" in
metal, wet the list with vinegar, reduced in strength conclusion:-"The sun's distance being 23984 radii
by water if slight action only is wanted, cover the of the earth, and the moon's only 6-the former is
wetted list with oilskin, and fasten it with the ribbon nearly 400 times the latter-lines, therefore, drawn
in desired part. About an inch of each extremity of from the sun to every part of the moon's orbit may
the strip of metal, must be left uncovered at each be regarded as very nearly parallel."
end, and be in contact with the skin. The cost of the
contrivance must evidently be rec koned in pence.
SUFFOLK AMATEUR.

THOS. EVANS, Stockport.

GALVANIC BANDS.

I do not know whether Sir John Herschel will be

R. L. J.

DR. TYNDALL'S EXPERIMENTS ON LIGHT. SIR, On trying the experiments on atmospheric dust particles, of which an account appeared in your SELF-CENTERING LATHE CHUCK. journal, it occurred to me to try the effect of inorganic take in his drawing of the self-centering lathe chuck SIR,-I think that "A. B." must have made a mis-particles, and for this purpose a piece of brown paper that appeared in your last issue. I see that the thread in the darkened room. A very small quantity of was ignited, and allowed to smoulder for a short time is left-handed in the chuck, where it screws on to the smoke (carbon particles) heightened the effects to a lathe mandrel. Now, I have seen a great number of romarkable and unexpected degree, and on a spirit chucks, and have used them myself, but I never before lamp being held four or five inches below a beam of either heard of or saw one with a left-handed thread; sunlight, the apparent cloud of smoke, before faintly directly the tool in the rest commences to cut the seen, was now strikingly manifest. piece of work fastened between the dogs, the chuck, raised to a red heat, showed the same effects. instead of tightening up on the mandrel, will screw off, unless the cut be a very small one; but if tighter the chuck would get. One with a left-handed it was a right-handed screw, the larger the cut, the screw might answer for a face-lathe, or more commonly called a chuck lathe, where by twisting the

ARTIFICIAL ICE.

An iron bar, S. T. PRESTON.

67, the annular nebula in Lyra o, M 13, the maguificent belt, the lathe can be reversed, aud using the slide. inquiry was made where ammonia apparatus for the

globular cluster in Hercules. Let us take them in the above order and give you our impression of them as we saw them on those admirable nights.

Aquile. I have divided this star more beautifully With a 2-sia. achromatic, by Wray, so of course do not mention it as a test for an 84in, speculum, but certainly the smallness of the discs and the large space between them, does surprise one who has been accustomed to telescopes of much smaller aperture; a power of 100 separated this star well.

Ophiuchi, Ophiuchi. The former a beautiful objeet, both easily divided; components with exqui

sitely small discs.

Crgui. A much more difficult object for a reflector than any of the previous stars, as it is of the third magnitude; however, on three of the evenings referred to, it was beautifully and completely divided, and frequently since that time, whenever the air was fine and steady, a power of 187 just split it, but 300 completely divided it. The division of this star gave me very great pleasure, especially as it was accomplished so easily and so neatly.

7 Cor. Bor. Very easy. 187 completely divided it; dises beautifully defined and exceedingly minute, with 300, black division was equal to 2, if not 3, diameters of one of the discs.

Bootis. Here was indeed the crowning test, as

rest at the opposite side to where it is usually used. I
think the chuck, on the whole, is a very useful one, it
saving a great deal of trouble in setting small work.

MARINE.

SHODDY MANUFACTURE.
SIR,-Seeing "Scrutator's" remarks in No. 255,
page 610, on the way in which I endeavoured to help
one of your correspondents with regard to the shoddy
manufacture, I was at once induced to look further

best encyclopædias on the subject. In this work, I
find that I am perfectly correct as to the machine
tator" goes further, and says, that allowing the ma-
used for tearing up old woollen rags, &c.- Scru-
chine mentioned to be correct as I take it, I have
still unanswered."
only "mentioned one of them, and therefore 1395 is
As far as the shoddy is concerned
the willey is the only machine used to reduce it to a
state fit for spinning. To go further into the matter
would be to give an account of the machines used in
spinning and weaving, &c. "W.M," the correspondent
who asked for the information, is apparently satis
fied; therefore, what business is it of Scrutator's "
to criticise that which is meant for others?

into the matter, and have since consulted one of our

The willey, which, he says, is used for opening raw cotton, is quite different from the one used in the

SIR,-In a late number of the ENGLISH MECHANIC production of ice could be obtained. I have one procured from Mignon and Rouart, 149, Rue Oberkampf, Paris, and have used it with perfect success several times. Some friends have had one in constant use for four years, and it never required repair or renewal of any sort. There are two sizes for domestic use, one costing 282f. or £11 6s., makes one kilogramme of ice in about two hours with the expenditure of about a double handful of charcoal, and pint of methylated spirit or less. The other makes 2 kilogrammes in 3 hours, and costs 406f., or £16 58. There are larger for manufacturing purposes.

J. B. YONGE, Mebourne, Winchester.

COLLIERY VENTILATION.

SIR. As a well-wisher of the ENGLISH MECHANIC, and as I desire to see its usefulness extended, I beg to suggest that colliery ventilation would be a good subject for discussion in its pages. You would thereby give some of our most intelligent working men an opportunity of recording their experience and giving their opinions.

To begin, would any brother reader oblige me with an honest reply to the following query:-Query; If the intake of a colliery should be 50ft. area, what should be the size of the return-with the mode or T. H. THOMAS. rule by which it is found?

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WHEEL-CUTTING ENGINE. SIR,-Through the kindness of a gentleman at Halifax, I am enabled to forward a very good photograph of a wheel-cutting machine for small work. BB is the bed, which is solid towards the left-hand end, and open to the right, to form a slide for carrying the upright part QEF, which is drawn along by a screw, of which the handle appears at H, to adjust for different diameters of wheels to be cut. Supposing the slide R R to be taken away, and W the wheel to be cut, the upright slide would first be brought to its place by turning the handle H, next the set screw C loosened, and the peg under it slid down to the circle of holes containing the division to be cut, and the peg of the alidade A brought to the same circle by sliding along the pin P till the index at I shows the right number. The stops SS are then adjusted, so that the lever TV, which works on a loose socket at T, may be able to swing sideways to the amount of the angle subtended by each tooth of W; and the machine being set going, the first cut is taken downwards by depressing the handle L, which may be made to rise again by hanging a weight to it over a pulley fastened to the ceiling. To move the division plate the required quantity for the next cut, the peg under C is first lifted by raising the end V of the spring lever T V against the pressure of the spiral spring D, and TV is then moved towards the right till it is stopped by S; and on letting go the lever the spiral spring D forces the peg at Cinto the proper hole in the plate. Next, by pressing on the head of D, the lever N presses against another lever (O) under the plate, lifts A up out of the way, and allows the plate to be moved round till T V comes in contact with the other stop S; and so on for each tooth in succession. M is a micrometer for adding a tooth when the division plate does not contain the precise number wanted- as, for example, in cutting 101 teeth with a division plate of 100 holes.

For bevel wheels the quadrant Q allows the upright slide to fall forward to any required angle, and for cutting teeth askew, as in the case of a worm-wheel, there is a centre at E on which the vertical slide can be swivelled over sideways. K is a hole in which a crane may be fixed to come over to steady the top of the arbor on which the work is held.

The picture shows the arrangement for rack-cutting, the whole length of the slide R R being itself a rack, into which the wheel W works. The lever L is found to work more agreeably than the screw which used to be at the top of F for moving the upright slide. J. K. P.

HOPKINSON'S VALVE.

SIR,-In reply to the inquiry of your Leamside correspondent of last week, I beg to inform him that the two valves act quite independently of each other; and the small one being regulated by a dead weight inside

the boiler, which cannot be tampered with whilst the steering a screw-vessel under canvas, with her pro latter is working, continues to blow off steam, no mat-peller down, especially if it be a three bladed one. ter how heavily the lever of the large one may be This is entirely obviated by the self-feathering screw, as the blades, when feathered, offer no twist to the GEORGE BATES,Agent for Messrs. Hopkinson and Co., passing water. for Durham and Northumberland.

weighted.

FOTHERGILL'S SELF-FEATHERING SCREW PROPELLER,

SIR,-The above screw is designed to supersede the necessity of hoisting up the screw in auxiliary screw vessels, when under canvas. It is entirely self-acting, requiring no hollow shaft or inside gearing, as in the case of the Bevis feathering screw; all its parts are concealed, so that no wreckage or floating material can jamb its action, its external appearance exhibiting no more peculiarity of form than an ordinary propeller. (Fig. 2) The principle is equally applicable to any kind of screw, whether two, three, or four

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blades. The boss is divided into three parts (Fig. 1), the forward part carries the blades for going a-head, the after for going asteru, immediately upon the engines stopping or upon the vessel over-running or outsailing her screw, the blades feather themselves into a line with the keel, and become useless. In regard to stowage of spare screw, and repairs of damaged screw, it has many advantages over the solid propeller, as its parts can be stowed separately, and a broken blade or other part re-supplied at once from the spare screw. All seamen know the difficulty of

It is anticipated that, now that the opening of the Suez Canal will render auxilliary steam power of more necessity than ever, that a screw on the above principle will be found a useful invention, especially in short-handed ships; and in all, when the expense and room of the screw-well may advantageously be

avoided.

The inventor has a 10in. in dia. model in gun-metal, which can be seen on application, by letter or other wise, to Watford,, Crick Station, near Rugby.

F..

HEATING GREENHOUSE BY GAS. SIR,-In reply to D. Bothroyd (Qy. No. 2067), I beg to state that the consumption of gas for heating the water-pipes in the greenhouse alluded to in No. 1708 has again been accurately tested by a dry meter (Glover, maker), and found to be 25 to 30 cubic feet per hour, according to pressure, which varies a good deal, and which is a very great disadvantage in the use of the most economical burner-the atmospheric-as so much depends on the proper proportions of air and gas previous to ignition so as to ensure as complete combustion as possible, and so prevent smoke or deposit of carbon. At 38. per 1000 cubic feet, the cost of gas in Bath, this is under 1d. per hour; and this winter, with the thermometer at 19° out of doors, the temperature inside the greenhouse was 46, at least 60% higher than required to keep the frost out. With the apparatus of Hertsman, of Bath, it could probably have been kept steady at 40, when the expense would not have averaged d. per hour. This very much coincides with the result of what "Professional," of Brighten, gives as his experience (see ENGLISH MECHANIC, page 637); only had he used 4in. instead of 3in. pipes, his quantity of heated water being larger, probably his result would have been in proportion.

Where there is no regular gardener or male domestic on the premises to attend to the fire of a flue late and early-for it is hardly work suitable for a female to feed either with coal or ashes-the gas (with an atmospheric burner properly fitted, and supplied with suitable mixture) will not only be found in every way more suitable, but cheaper. A man up at 12 and 4 a.m. is not long fit for his usual day's work. If the common gas-burner is used, the expense will be very much greater, and the result less.

Can Professional" give the address where a simple good gas pressure gauge, to be attached to the meter, can be obtained? This would be of much value to consumers generally.

A very simple and cheap method of keeping frost out of a moderate-sized greenhouse is by an Arrot stove of the right sort, with an upright pipe of in., by

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