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click T whose pivot is set in the frame, preventsto the crank-pin, and the piston-rod is kept upthe larger ratchet from falling back, and so the right. spring SS' still drives the great wheel during the time the clock takes to wind, as it need only just keep the escapement going, the pendulum taking care of itself for that short time. Good watches have a substantially similar apparatus.

122. A very convenient construction of parallel ruler for drawing, made by cutting a quadrangle through the diagonal, forming two right-angled triangles A and B. It is used by sliding the hypothenuse of one triangle upon that of the other.

123. Parallel ruler consisting of a simple straight ruler B, with an attached axle C, and pair of wheels A A. The wheels, which protrude but slightly through the under side of the ruler, have their edges nicked to take hold of the paper and keep the ruler always parallel with any lines drawn upon it.

124. Compound parallel ruler, composed of two simple rulers A A connected by two crossed arms pivotted together at the middle of their length, each pivotted at one end to one of the rulers, and connected with the other one by a slot and slidingpin, as shown at B. In this the ends as well as the edges are kept parallel. The principle of construction of the several rulers represented is taken advantage of in the formation of some parts

of machinery.

125. Parallel ruler composed of two simple rulers A B connected by two pivotted swinging arms C C.

126. A simple means of guiding or obtaining a parallel motion of the piston-rod of an engine. The slide A moves in and is guided by the vertical slot in the frame, which is planed to a true surface.

127 differs from 126 in having rollers substituted for the slides on the cross-head, said rollers working against straight guide-bars A A, attached to the frame. This is used for small engines in France.

128. A parallel motion invented by Dr. Cartwright in the year 1787. The toothed wheels C Chave equal diameters and numbers of teeth; and the cranks A A have equal radii, and are set in opposite directions, and consequently give an equal obliquity to the connecting rods during the revolution of the wheels. The cross-head on the piston-rod being attached to the two connectingrods, the piston-rod is caused to move in a right

line.

129. A piston-rod guide. The piston-rod A is connected with a wrist attached to a cog-wheel B which turns on a crank-pin, carried by a p late C which is fast on the shaft. The wheel B revolves around a stationary internally toothed gear D, of double the diameter of B, and so motion is given

130. The piston-rod is prolonged and works in a guide A, which is in line with the centre of the cylinder. The lower part of the connecting-rod is forked to permit the upper part of the piston-rod to pass between.

131. An engine with crank motion, the crankwrist journal working in a slotted cross-head A. This cross-head works between the pillar guides D D of the engine framing.

132. A parallel motion used for the piston-rod of side lever marine engine. FC is the radius bar, and E the cross-head to which the parallel bar E D is attached.

133. A parallel motion used only in particular cases. (To be continued.)

IMPROVED SCREW DRIVER.

TH THE device of which an engraving is given, secures increased leverage at the will of the workman without increased length, and will for many kinds of light work also take the place of the bitstock or brace for drilling, boring, &c.

having a recess to receive and retain, when not! In the engraving A represents a wood handle, in use, a second and smaller point, B. This

B

and the counterparts of the clutch at D engage with each other. The shank will then turn with the handle, and may be used precisely like the ordinary screw-driver, except that when it is necessary to use the power of both hands in driving home a large screw, an increased leverage is gained by the curvature of the shank.

It will also be obvious that bits properly formed may be placed on the end of the large screwdriver in the same manner as the supplementary point B above described, when the instrument will take the place of the ordinary bit-stock.

David Drummond, of McGregor Iowa, U.S.A., is the patentee.

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recess is indicated by the dotted line. This complete; Fig. 4 is a back-end elevation of the supplementary point has a sleeve, indicated by a main slide; Fig. 5, the screw at back; Fig. 6, a dotted line, which slips over the point of the side elevation, and Fig. 7 a front-end elevation of larger screw driver. The shank C of the larger screw-driver is bent the main slide; Fig. 8 is the side elevation of the in the form shown. At D is a clutch, one portion slide in section, showing also the position and of which is formed on the shank, and its counter-arrangement of the traverse screw; Figs. 9, 10, part on the handle, and underneath the ferrule. and 11 are elevations of the second slide; Figs. The extremity of the shank C in the interior of the handle, has a turned groove, into which the point of the screw E enters, and holding the handle so that the two portions of the clutch cannot engage with each other, permits the shank to be revolved like an ordinary bit stock.

13 and 13 show the nut for traversing this slide; Fig. 14 shows the second traverse screw; Figs. 15 and 16 give the nut for this screw; Figs. 17 and 18 are elevations of the slide which carries the tanCgent wheel; Fig. 19 is also an elevation of the same slide, but in this the slide and tangent wheel a shown in section. This Fig. also shows themes of attaching the tangent wheel to the slide; is a plan of this slide and tangent wheel ;

When it is desired to use the tool with one hand, the screw E may be turned ont a little distance, when its point no longer enters the groove,

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is the endless screw for gearing into the tangent | third slide, a slide which is fastened to the tangent
wheel; Figs. 22 and 23 show the lugs or bear-wheel; Fig. 27 is a plan of this slide; Fig. 28
ings which carry the endless screw-the nuts of is the traverse screw for this slide; Figs. 29 and
these lugs are recessed into the underpart of the 30 show the nut belonging to this traverse screw;
slide; Figs. 24, 25, and 26, are elevations of the Figs. 31 and 32 are elevations of the top slide,

which has a boss or socket for receiving the too slide; Fig. 33 is a plan of this slide; Fig. 34 is the nipping screw for ho'ding the tool slide in position; Figs. 35 and 36 are elevations of the tool slide; Fig. 37 a plan of the slide; Fig. 38 is

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one of the side stops; Figs. 39 and 40 show the or lug, which is attached to the tool slide; Figs. 41 and 42 are elevations of the tool receptacle; Fig. 43 is a plan of the tool receptacle, which shows also the opening for inserting the holding nuts; Figs. 44 and 45 show the holding-down nut, of which there are two; Fig. 46 shows the nippingscrew for one of these nuts; Fig. 47 is the screw for the other nut, the top part of which is differently shaped to receive the lever for moving the tool into cut-this lever is shown at Figs. 48 and 49; Figs. 50 and 51 show the two screws for regulating the cutting depth for the tool; Figs. 52 and 53 show the lug nuts for these screws; Fig. 54 is the small screw which is used for nipping the two regulating screws; and Fig. 55 is a stud, which forms the fulcrum for the forcing lever. W. H. N.

THE SCREW. This mechanical power is generally so fully described in elementary works on mechanics, that we may dismiss it with a few remarks.

As the screw with a rectangular thread may be described to be a cylinder round which is wrapped a triangular plate of uniform thickness, from which the lower portion is cut away so as to leave a projection of uniform breadth and depth whose upper and lower surfaces project at right angles to the surface of the cylinder at every point, we see that the screw is merely a modification of the "inclined plane," for it is clearly a matter of indiference, with regard to the forces engaged, whether we urge the body up the inclined plane or force the inclined plane under the body.

Suppose now the screw to be placed vertically, let i he the angle of inclination of the thread to the horizon, P' the power applied horizontally at the circumference of the screw, and W the resistance overcome acting vertically, then, reerring to Vol. X., page 598, we have

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EXAMPLE 17. A circular block of dressed granite (specific gravity = 26), 3ft. in diameter, and lft in height, rests on a rough horizontal plane; if the coefficient of friction = , and the block be capable of a motion only of rotation round a vertical axis, passing through its centre of figure, calculate the magnitude of the force, which, applied tangentially at its circumference, will suffice just not to move it.

ASTRONOMICAL NOTES FOR JUNE.

BY A FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY THE Right Ascension of the Sun at Greenwich Mean Noon on the 1st of June is 4h. 36m. 34 47s., and his North Declination 220 4' 12". He is therefore situated to the North of Aldebaran and the Hyades, and not very far from the small star Tauri (vide map of "Eastern Sky," Vol. X p. 64). His meridian altitude is now very considerable, attaining its maximum on the 21st of the month, when at his culmination in London he will be nearly 620 high. The Sun rises in London on the 1st at 3h. 51m., and sets at 8h. 4m.; so that the day is 16h. 13m. long. On the 21st (the longest day) the Sun rises at 3h. 44m., and sets at 8h. 18m., so that he is 16h. and 34m above the horizon. From the cause explained on p. 159 of the present volume, there is no real night in any part of the United Kingdom during the present month in fact, in the extreme North of Scotland, small print may be read easily enough now up to nearly 11 p.m. The equation of time on the first day of June is 2m. 29 71s., and is to be subtracted from the hour indicated by a sundial to obtain that which a properly-regulated clock ought to show. The equation diminishes to 6-14s. on the 14th, after which it becomes additive, and on the last day of the month, 3m. 29-628. must be added to apparent noon to obtain the mean time at the instant of its occurrence.

The Moon enters her First Quarter at 11h. 16:3m. on the night of the 6th; is Full at 1h. 47 2s. in the afternoon of the 13th; enters her Last Quarter at 9h. 358m. on the evening of the 20th, and is New at 11h. 33 2m. p.m. on the 28th. She is in Perigree on the 11th at 1 p.m., and in Apogee at Noon on the 23rd. Her age at Noon on the first is 2-1 days, at Noon on the 2nd 31 days-and so on. At 2 o'clock in the afternoon of the 4th, Libration will bring an additional portion of her surface into view in her S.E. quadrant. At 4h. a.m. on the 22nd, more of her S. W. surface will come into sight from the same cause; aud finally, at 15h. on the 30th (or, speaking ordinarily, at 3 o'clock in the morning of the 1st of July), the South Easterly portion of her surface will, for a similar reason, be once more seen in excess. The Moon will be in conjunction with Uranus at 5h. 41m. on the afternoon of the 2nd, of course in brilliant daylight. At 59m. past 6 on the 15th she will be in conjunction with Saturn; at 935 a.m. on the 25th with Venus; at 8-22 on the 26th with Mars, and 41m. later with Jupiter. She will be in conjunction with Mercury at 49m. past 2 a.m. on the next morning, and finally, once more with Uranus at 14h. 43m. on the 29th. Three stars only, of the 6th magnitude, or larger, will be occulted during June. The first occultation will be of Libræ on the evening of the 11th. The star will disappear at the Moon's dark limb at 9h. 43m., and reappear at her bright limb at 9h. 51m. On the night of the 18th, B. A. C. GOSS will disappear at the bright limb at 11h. 55m., and reappear at the dark limb at 12h. 38m. Lastly, on the 16th, Capricorni will disappear at the Moon's bright limb at 12h. 50m. a.m. and reappear at the dark limb at 13h. 58m.

Mercury is practically invisible for the first third of the month, being too close to the Sun. He Souths only about 19m. after Noon on the 1st, and is in inferior conjunction with the Sun on the 4th. Towards the end of June he becomes a Morning Star, and is on the Meridian about halfpast 10 a.m. on the 30th. Venus is a Morning Star throughout the month. She Souths on the 1st at 34m. past 9 a.m., and on the last 17m. past 9. She is becoming. less interesting as a telescopic object, and it is getting ap parently smaller daily. She travels during June through Aries, and the greater part of Taurus. Mars is still a Morning Star too, Southing at 10h. 43-4m. a.m. on the first day of the month hand at 10h.15m. a.m. on the 30th. He is passing through

Taurus, and is in conjunction with Jupiter at 7h. 12m. on the afternoon of the 27th. Jupiter is a Morning Star likewise, and too close to the Sun to be well seen. Owing to this proximity the phenomena of his satellites are invisible. He is on the Meridian on the morning of the 1st only, about 25m. before Noon, and on that of the 30th about 9m. past 10. Jupiter will remain in Taurus during the entire month. Saturn, were he not so very low down, is now conveniently situated for observation. He is on the Meridian at 13h. 2.9m. on the night of the 1st, and about 11 on the last night of the month. He continues on the N.W. confines of Sagittarius. He is in opposition to the Sun at 5m. past 4 in the afternoon of the 16th. His rings being now practically at their greatest opening, he presents (under favourable atmospheric conditions) a telescopic object of the very highest interest. Uranus, still in Gemini, and Neptune, on the confines of Pisces and Aries, are both too close to the Sun to be visible.

June is the month in which the smallest number of Shooting Stars has been observed; and would appear to be the one most free, of all the twelve, from the apparition of these phenomena.

LETTERS TO THE EDITOR.

We do not hold ourselves responsible for the opinions of our correspondents. The EDITOR respectfully up as briefly as possible.]

requests that all communications should be drawn

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

which are rather drawbacks when applied to a refractor. Your back volumes contain some illustrations from which " Scorpio" may derive many useful hints. The simplest way to calculate the diameter of the field of a Huyghenian eyepiece is to set the telescope so that a star shall cross the field accurately on a diameter, and to note the seconds and fractions of a second which it occupies in doing so. Then this interval in time x 15 x cos. star's declination the angular diameter of the field. I append an example, as requested. It is worked by logarithms to obviate the necessity for half a column of mere common multiplication. Suppose that your correspondent has observed the transit of Regulus diametrically over the field of his Huyghenian eyepiece, and has found that it occupied 1m. 8:48. by a sidereal clock in crossing it, then the calculation would stand thus:

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log. of 1001-29

3-0005602: that is to say the angular diameter of the field of his eyepiece is 1001-29 or 16' 41 29. I have employed seven places of decimals, but five will be ample in practice. It will be further pretty evident that if we were observe a star on the Equator, the operation would resolve pied in its passage by 15, to convert them into seconds itself into multiplying the seconds of sidereal time occuof arc, as there is, obviously, no allowance to be made for declination. Stars like Orionis, Virginis, Virginis, Virginis, a Aquarii or K Piseium, will furnish results quite sufficiently accurate for my querist's requirements, when treated in this way. I need All eheques and Post Office Orders to be made pay- scarcely add that this determination must be made able to J. PASSMORE EDWARDS. afresh with each new object-glass to which the eyepiece is applied. Next, the webs in a transit eyepiece I would have every one write what he knows, and are enclosed in a tube, but are only "protected" by as much as he knows, but no more; and that not in the care of the observer. It is not considered de rithis only, but in all other subjects: For such a per-gueur in the best observatories to poke your fingers son may have some particular knowledge and expe- through them. "Scorpio" must read the reply given above rience of the nature of such a person or such a foun- to" E. M. B." with regard to the Pancratic Eyepiece. tain, that, as to other things, knows no more than The Cambridge (U.S.) Refractor is of 14 92in. aperture, what everybody does, and yet to keep a clutter with and 22:38ft. focal length. The Great Melbourne rethis little pittance of his, will undertake to write the flector, a Cassegrainian of 30 5ft. focal length, and 4ft. whole body of physicks: a vice from whence great in- in clear aperture, will be found described in great conveniences derive their original. -Montaigne's detail with engravings in Vol. VIII. of the ENGLISH Essays. MECHANIC (No. 194), pp. 247 to 252. "Scorpio should certainly buy the volume containing the description referred to, if he be interested in this monster

THE USE AND CONSTRUCTION OF THE
TELESCOPE.

SIR,-If "Herbert," p. 204, will look through the ENGLISH MECHANIC from its commencement, he will find that his idea is by no means a novel one. It last appeared in its only practical form on pp. 73 and 152 of your tenth volume.

Mr. A. W. Blacklock (on the same page) will perhaps forgive me for pointing out that he observed Ursa Majoris with 10in. of aperture-I with 4. I must also ask the forgiveness of "J. V. B.," p. 211, when I express my conviction that an account of a few words uttered by Mr. Buckingham at the Royal Astronomical Society, contained in some journal unnamed and unknown, can scarcely be held to be strictly a “definite report of the optical performance" of his telescope.

If "Turton (3797), p. 215, wants merely a simple stand, he will find a detailed description of a rough but effective form of Equatoreal mounting at p. 394 of your second volume. The best kind of Equatoreal with which I am acquainted is certainly that of Cooke, of York. The description of the water clock of Lord Rosse-then Lord Oxmantown-will be found at p. 265 of vol. 26 of the Royal Astronomical Society's "Monthly Notices."

I may inform "E. M. B." that a pancratic eyepiece is nothing in the world but a common terrestrial one, with a provision for separating the double combinations at the eye-end from that at the object-end; the farther these pairs of lenses are removed from each other the greater being the power acquired. If my querist will refer to Vol. III. of the ENGLISH MECHANIC, he will find a diagram in a letter by Mr. Moss (Fig. 2) on p. 381, which will illustrate this. Assuming him to have this diagram before him, I need only observe that when the combination CD is pushed towards the combination A B the power is diminished. When, on the other hand, they are separated, the power is increased. This eyepiece would screw into the adapter of a Newtonian telescope, just as an ordinary Huyghenian one does; but I should not expect it to be, in the least degree, a practically useful form with that instrument. I may say, in reply to your correspondent's second question, that the lenses of the Ramsden eyepiece are of the same focus, but not of the same diameter, the eye-lens being the smaller of the two. In an eyepiece of this construction now before me, the diameters of the eye and field lenses are as 4: 7.

Turning now to the letter of "Scorpio" on p. 234, I find a mixture of queries which, with his permission, I will reply to separately under their appropriate headings. Imprimis, though, I should remarkably like to know the exact value and meaning of the assertion that "All Solomon's £5 telescopes are warranted to show five stars in the trapezium Örionis." Suppose (rather a wild supposition, by the way) that I bought a £5 telescope, and failed to see the fifth star in the trapezium with it, should I have my money returned, or be told that my own eye was in fault, or what? Again, before proceeding to answer your correspondent's questions, I must just remark that turning back to the page he specifies I certainly find that I am there made to speak of 2-5 as the limit of separating power of a 24in. telescope, but I wrote 2" 0, and the must have got turned into a 5 in the press. Beginning now with his third query, as the first having reference to the telescope, I may tell him that one great difference between the mounting of a reflector and that of a refractor, is that the latter is supported about the middle of its length; while all the weight of the former being at the bottom of the tube, it has to be held near that part of it. This necessitates a compacting and compressing of an Equatoreal mounting for a reflector, bringing it all, so to speak, near the ground, and a general massiveness in the details

instrument.

"

The formula for obtaining the geometrical focus of a double concave lens is simply this, divide twice the product of its radii by their sum. Or, more simply, in the case of a double concave lens of glass of equal curvatures, the principal focus is at the centre of the first surface. I cannot think of any method of determining such focus practically. Perhaps opticians have some way of doing this, and one of them might enlighten us.

Mr. Baguley (3853), p. 238, almost answers himself. The large telescope, from the spherical aberration of the object-glass remaining uncured, would give a quantity of overlapping images which must inevitably be fatal to sharp definition. It scarcely requires one to rise from the dead to announce authoritatively the fact that a small object-glass which is good, will always give clearer and crisper definition than a larger one which is bad.

Mr. Walter Jones (3899), same page, should really treat himself to set of our MECHANICS. He will find his question answered over and over again, so far as it is susceptible of a reply, in former volumes. A FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY.

ASTRONOMICAL.

SIR,-The doctors" who "disagree,” in the case to which "Ab Initio," refers on p. 207, are the Thanet Guardian, and "The Nautical Almanac ; " from the latter of which I obtained the data on which I founded my replies on pp. 525 and 579 of your last volume. The "Establishments of the Ports" for the different localities given on pp. 496 and 497 of the National Ephemeris, are reckoned from Apparent Noon. The tides at London Bridge are given for Mean Noon; but as the Establishment of the Port for London is obtained in the same way as that for Margate, or anywhere else, the difference remains constant. I really do not see what I have to add to what I said on p. 579 of Vol. X. If I rightly remember the request of "Saul Rymea," and my present correspondent, it was that I should myself furnish tide tables; but I really must ask to be excused for declining to wade through a mass of the most merely mechanical computation. Why does not "Ab Initio "undertake it himself? He will find it a Tidy little job.

The mention of the "Nautical Almanac " brings us back to "Scorpio" and his string of questions on p. 234. Noticing now those having more special reference to Astronomy, I may tell him that the "Nautical Almanac" is published by John Murray, of Albemarle-street, London, and that its price is half-a-crown. Any bookseller will procure it. It contains the R.A. and Dec of 147 fixed stars. The object of your correspondent, however, in asking for particulars of a book containing Right Ascensions and Declinations, is probably that he may be enabled to find objects of interest in the Heavens. If such be his intention let him get forthwith Webb's "Celestial Objects for Common Telescopes;" it is published by Longmans and Co., London, for 7s. 6d., and is essentially the book which the incipient amateur will find indispensable. "Scorpio" asks for a "moderately cheap" work, but if he will take my advice and buy the book I recommend him, I shall feel grievously disappointed if he does not consider it dirt cheap, when he sees what a mass of information it contains. The map of the Moon alone is honestly worth 58. out of the 78. 6d. Turning to a third question, I may briefly say that Kepler's third law is not rigidly exact, because of the perturbations caused by the various bodies of the Solar system, inter se; but that it is sufficiently nearly so to get an excellent approximation in any given case, where either the periodic time, or the mean distance is known.

"

Surely the "Cluster" figured by "Aristotle" (3874). p. 238, cannot be meant for the Pleiades? and yet. the Stagyrite speaks of it as a " cluster," and having lately disappeared in the West." With regard to my Map, on p. 64 of your last volume, I can only say that, when I drew it, the Pleiades occupied the precise position I have there indicated; and that although just now I walk by faith and not by sight in the matter, I have not the very slightest doubt that, at this present writing, they are in exactly the same place, as they were then.

A FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY.

THE ENGLISH MECHANIC LIFEBOAT. SIR, Will you permit me once more to appeal to my fellow-subscribers for their more cordial co-operation in the matter of the lifeboat? Though much disappointed, I cannot yet believe that they are really indifferent, and positively refuse to lend a helping-hand to this Godlike work. Comrades! will you longer shirk your responsibility? Can you allow a few of us to struggle on, hoping almost against hope, when a single united effort from you would make our hearts rejoice, and be the means of saving numbers of fellowcreatures' lives? The refrains of two of the songs sung at our concert are still ringing in my ears :"Then three times round went our gallant ship, And three times round went she;

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Our undertaking, though important, is not difficult, if only a reasonable proportion of subscribers will help. It is not even novel in itself, unless we make it so by either unprecedented success or signal failure. Other journals have their lifeboats, and why should not we? I find Routledge's Magazine for Boys has subscribed £306 12s. 6d., and built one lifeboat; the Dundee People's Journal has subscribed £822 158. 10d., and built two lifeboats; and the Quiver has subscribed €1878 18. 11d., and built three lifeboats. It is my belief that the ENGLISH MECHANIC can do more than any of these, and with all my heart I will make one to say that it shall.

GEO. LUFF, Staunton Harold, Ashby-de-la-Zouch.

P.S.-Success to the Mutual Improvement Societies! Country residents are almost powerless to aid in such matters, or I should be delighted to join in the movement. I know it would be a great boon to me could I discuss certain subjects appearing in the MECHANIC with a few kindred (but more practical) spirits. I ask if our mechanical friends at Derby could not attempt a branch?

KAS

May

SIR,-In the black days of the Cotton Famine a celebrated" Launcashire lud "-viz., the late Lord Derby -wrote to the Times in these forcible, if not elegant, words :-"Can yo help us? We be clemming "-i. e., starving. I quote these memorable words of our "Rupert of debate" in behalf of "poor Jack," substituting "drowning " for "clemming." It was said or sung by Dibdin that

"A sweet little cherub sits up aloft, And looks out for the life of poor Jack." This may be quite true, although how he manages to sit at all, with his peculiar conformation, is a mystery past my solving, assuming ye cherub's portrait in our old City churches to be accurate in detail; so I must leave it to Owen or Huxley. But as we can hardly, expect the aforesaid cherub to don a cork jacket and sit on the thwarts of a lifeboat, or any conceivable number of cherubs, to man it; and even if they could, having no arms, to row, it would be impossible to them. I think it logically follows that instead of trusting to the assistance under difficulties which cherubs may afford, we ought to provide the lifeboat ourselves, trusting there will be no want of stout arms and stout hearts, able to sit in and row it on its blessed errand at need.

I am in no sense of the words a clever beggar, but however my friends may doubt the fact, and think it

quite impossible that one so lamentably addicted to chaffing" can be in earnest, I do assure my fellowreaders that I am terribly in earnest in the matter of the lifeboat, and do most earnestly entreat them to aid and assist this meritorious attempt to provide the means of saving the life not only of poor Jack, but the ship's passengers also; and I trust they will stamp it with their approval in the most effectual manner possible by sending at least one I hope many more than one-stamp of her Majesty's kind countenance impressed on gold, silver, or paper; for the precious metals are doubly precious when employed on works of mercy and benevolence. If the constable is legally empowered to call on all good men and true to aid and assist, in the Queen's name, to keep the peace, how much more are we morally empowered to call on all good men and women also to aid and assist this good work.

I have before said I am not a clever beggar-sooth to say, begging is not my forte-but I trust the want of ability in the solicitor may not in this instance cause any injury to the case. What is impossible to one is easy to many; and we English mechanics are manyenough, surely, to do what Capt. Busk has done singlehanded-viz., to launch one lifeboat. It only wants the will-and I trust we have enough of that to prevent the captain's princely liberality from "making us ashamed.' THE HARMONIOUS BLACKSMITH,

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SMALL SLIDE SCREW CUTTING LATHE. SIR-We beg to send you above a photograph of a small description of screw cutting lathe, which we have lately constructed.

This lathe is constructed with bed on the triangular bar principle, cast hollow to receive the leading screw, which is thus protected from dust and injury. The mandrel head is fitted in the usual way with back gear, the mandrel of the steel running in double conical collars of hardened steel. Compound slide rest. Full set of change wheels, and arrangement for cutting screws of right and left hand thread to any pitch. This lathe complete weighs about 2cwt., and runs very easily with the foot wheel and treadle BOOTH, BROS, Engineers, Dublin.

motion.

CONVEXITY OF WATER. SIR,-Your readers who have been interested in these experiments will be aware that Mr. Carpenter's argument for the non-convexity of the canal was entirely based on the equidistant appearance of the signals in the field of view when looking through the cross-air telescope. Now, so far from this proving that the canal was flat, it proves exactly the opposite, as the subjoined diagram will show.

5. What degree of exhaustion is necessary to pro duce the phenomena mentioned in the former part of my letter?

Theoretically considered, Grove's plan seems to me the simplest and best. Can anyone describe minutely (for I make all my own instruments) its construction? I know its general principle, as described in scientific books, but I want one to work by. In return for such information, I can give your readers such information on the construction of induction coils as I know they cannot get anywhere else in England. I have a plan of construction, so simple, and yet so effective, that I get such results as have never been yet obtained by any maker. I have one just containing only 4 miles of secondary, and yet with one small Grove's battery with the platina only 4in. by 2in. I produce splendid sparks 4in.in length. Any information on the above subject to the purpose will INDUCTORIUM. greatly oblige.

WRAY'S 20-INCH O. G. SIR,-Inquiries have been made in your columns as to the performance of the above glass now in the possession of Mr. Buckingham, and the only answer as yet given has been by " F.R.A.S.," to the effect that with regard to its optical quality we have no definite report." In the absence of this, perhaps it may be interesting to some of your readers to have the maker's own report in a letter to the Astronomical Register in -A' Aug., 1867. It is as follows:-" Sir,-Permit me through your pages to inform Mr. Darby that the new 20in. clear aperture object glass which I have just furnished for Mr. Buckingham shows ya Andromeda separated with all powers above 200, and that with a power of 450 the distance between the components is much wider than in proportion to Mr. Dawes's diagram, evidently showing that the separating power depends mainly on the size of the aperture, &c. To the 20in. object glass just finished Herculis and Cygni are astonishingly easy objects. We have not as yet had time to make much scrutiny, but the most difficult tests have hitherto, with the full aperture, been instantly resolved even in an indifferent state of the W. WRAY." atmosphere.-I am, &c.,

C.

Let A B C be objects which appear equidistant in the field of view of telescope. A is the hair line in the telescope; B is the signal 3 miles distant; C is the signal 6 miles distant. Join A A', A B B', and A Cas represented by the dotted lines-the angles subtended by these lines are equal. Now join A B C, the points The line which are equidistant in the field of view. that joins them cannot be other than convex.

VERAX.

THE AIR PUMP.-THE HIGHEST VACUUM. SIR,-Can any of your scientific readers assist me in the following difficulty? I have a large doubled-barrelled air pump, which I bought in order to produce such vacuo as would exhibit the phenomena of the induced current in vacuo. I find, however, that I cannot get a vacuum good enough to show Gassiot's fountain, the Aurora tube, or the rotation of the electric light round the magnet. Now if some of your practically scientific readers can and will answer the following queries, I shall be deeply obliged. I say practically scientific, because, theoretically, I know as much about the subject as most, but I want the opinions and advice of someone who has done himself what he recommends and not merely taken it undigested from books, most of which I have read.

1. What is the highest vacuum, as indicated by the syphon gauge, that an ordinary, well-made doublebarrelled air pump, with oiled silk valves, is capable of producing?

2. Is there any way of adapting other valves, such as Babinet's plan, so as to produce a better result.? 3. The machine admitting it, could not an extra barrel on some other plan, such as Grove's or Newman's be adapted so as to produce the higher vacua? 4. If so, which is the best, simplest, and most effective? and would your correspendent describe its construction practically?

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CHERRY STONING MACHINE. SIR,-I send a clipping from the Scientific American illustrating a new cherry-stoner.

It is screwed to the table by a hand screw A. An upright B supports the body of the machine. The fruit is held in the left hand as shown in the engraving, and rolls down along a gutter C, and enters the small cups in the periphery of the annular wheel D.

E is a double crank from which a link F imparts vertical reciprocating motion to the cross bar G, and also to the recurved punching bar H. Each time the cross bar G rises, a stud engages with one of the cups on the annular wheel D, turning it along oneeighth of a revolution, and bringing another cup directly under the point of the punching bar H, carrying with it the fruit which has fallen into it from the gutter C. Each of the cups has a hole through the bottom large enough to permit the passage of the pit; and when the punching bar descends by the rotation of the crank, it pierces the fruit and forces the pit through the bottom of the cup, into the chute J, whence it falls into a dish placed to receive it.

Thus the pits may be removed almost as fast as a child can turn the crank, aud the operation is so rapid that the juice does not escape, and the fruit retains its natural shape and appearance.

This invention is manufactured by Geer, Stewart and Brother, Galesburg, Illinois, U.S.

КАРРА.

READINGS FROM THE GLOBES. SIR,-One of the consequences of the rotation of the earth upon its axis (which we take for granted as having been proved) is that man, animals, trees, and atmosphere are carried round with it from W. to E. at different degrees of swiftness, according to their proximity to the equator; but the rotation is so rapid and silent with which we proceed, that none of us can feel it, for the earth rotates "With inoffensive pace that spinning sleeps On her soft axle, while she paces even,

FIGI

E

A

B

A

E

And bears thee soft with the smooth air along.' By reference to Fig. it will be easily seen that whil'e she spins on her axis PP from west to east, tho se who live at the equator E E must be carried around with much greater velocity than those living on the parallel, A A, and these again than those living at B B, while the pole will have scarcely any motion whatever. This will be readily understood by turning round a terrestrial globe, and having once ascer tained the length of a degree on the earth's surface, we can then know at what rate per hour any point on the earth proceeds, and it is a matter of considerable nicety to determine the length of a degree, which has been found to vary a little, and to be longer near the pole than the equator. The importance of an accurate measurement of the number of miles in a degree cannot be too highly estimated, for upon it the great Newton founded his theory of universal gravitation, and he was for some time prevented from propounding it from the inaccurate measurement of his age; but for the sake of illustration we will take it as commonly estimated 69 miles in a degree. Now, as the globe completes its rotation in 24 hours, it of course passes through 15 every hour, and by multiplying 69 by 15 we get 1042 5 miles per hour, which is more than 1 mile per second. This is speaking of its actual rotation through 360°, or till it arrives opposite to the same fixed star from which it started, but in reality it revolves nearly 361°, because the sun has a motion of its own, having proceeded about this distance on its annual course in the interval. This, then, is only a close approximation to the actuality. We have seen that the parallels of latitude differ in length as they approach the poles, and consequently London is carried round with less velocity than Quito. If we wish to ascertain its speed we must find the number of miles in a degree in this parallel-namely, 51, which is done by measuring the distance between the meridians 15° apart, which is equal to 94, and then we have a simple proportion sum-15°: 9°:: 69 miles: 43, which gives 645 miles per hour as the rate at which London revolves. The most accurate way, however, of determining the number of miles in a degree in London's latitude, is by an easy formula in trigonometry-R: 69:: cos. 51: x. Thus:log. 69-5 = 1-841985 cos. 51° 30′ = 9.794150

11-636135 Subtract R. 10-000000 1-636135

which answers to the natural number 43-26. Thus we find that the number of miles in a degree varies, for whilst at the equator there are 693 in one degree, in the latitude of London there are 43 26, but at the poles 0. These results have been verified by actual

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