Abbildungen der Seite
PDF
EPUB
[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed]

right.

MECHANICAL MOVEMENTS.

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 spring S S 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 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

line.

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.)

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.

THE LATHE AND ITS USES-THE SPHERICAL SLIDE-REST.

W IMPROVED SCREW DRIVER. THE HE device of which an engraving is given, workman without increased length, and will for secures increased leverage at the will of the 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.

B

This

E give this week very complete working drawings of the slide-rest for spherical and curvilinear work, described in the ENGLISH description of the rest was then given, it will MECHANIC for November 19th. As a full general suffice if we now simply explain the various detailed figures.

Fig. 1 gives a side elevation; Fig. 2 an end 'elevation; and Fig. 3 a plan of the slide-rest

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 dotted line, which slips over the point of the larger screw driver.

main slide; Fig. 5, the screw at back; Fig. 6, a side elevation, and Fig. 7 a front-end elevation of 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 13 and 13 show the nut for traversing this slide of the handle, has a turned groove, into which Fig. 14 shows the second traverse screw; Figs. 15 the point of the screw E enters, and holding the and 16 give the nut for this screw; Figs. 17 and handle so that the two portions of the clutch can- 18 are elevations of the slide which carries the tannot engage with each other, permits the shank Cgent wheel; Fig. 19 is also an elevation of the same to be revolved like an ordinary bit stock. slide, but in this the slide and tangent wheel a When it is desired to use the tool with one shown in section. This Fig. also shows themes of hand, the screw E may be turned ont a little dis-attaching the tangent wheel to the slide; tance, when its point no longer enters the groove, is a plan of this slide and tangent wheel ;

[merged small][graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][merged small][merged small][merged small][merged small][merged small][subsumed][subsumed][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small]
[ocr errors]

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

[graphic]

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 528, we have

where r is the radius of the screw.

This formula can he put into a form which contains the lineal dimensions of the screw alone. Let be the pitch" of the screw, or distance from any point of one thread to the corresponding point on the next, measured parallel to the

[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]

From the above formula for the friction of a pivot, we see that in the screw, when the friction on the end as well as the friction on the thread is taken into account, that

where is the radius of the end or pivot.

Frequently we support a vertical shaft by means of a collar, as in Fig. 18. In this case the surface of contact between the collar and its support is clearly an annulus,

whose external radius is the radius of the collar, and the radius internal radius of the shaft.

In Fig. 19, let CA, the radius of the shaft,, and C B the radius of the collar,

R, then the element of area is in this case a trapezium A B D E, the plessure in which acts through its centre of gravity, equal to which is situate at a distance R2+R+ 1.2

[ocr errors]

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. Satoru, 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.

which are rather drawbacks when applied to a refrac-
tor. 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:-
68.48. log.
1-8350561
15 log. 1-1760913

June is the month in which the smallest number of Shoot-
ing Stars has been observed; and would appear to be the
one most free, of all the twelve, from the apparition of these Dec. N. of Regulus 12° 36′ log. cos. 9-9804128
phenomena.

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.

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 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 are enclosed in a tube, but are only "protected" by the care of the observer. It is not considered de rithrough them. "Scorpio" must read the reply given above to E. M. B." with regard to the Pancratic Eyepiece. The Cambridge (U.S.) Refractor is of 14 92in. aperture, and 22:38ft. focal length. The Great Melbourne reflector, a Cassegrainian of 30 5ft. focal length, and 4ft. in clear aperture, will be found described in great detail with engravings in Vol. VIII. of the ENGLISH 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 instrument.

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 per-queur in the best observatories to poke your fingers son 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.

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. 78 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 Orionis.' 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

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 ; 99 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 " back to 66 brings us 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;

And

For the want of a lifeboat they both went down, As she sunk to the bottom of the sea."

"They're in the boat! they're all afloat! Hurrah! they've gained the shore! Bless the lifeboat! bless the lifeboat! Oh, God, thou'lt hear our prayer! Bless the lifeboat! bless the lifeboat!

No longer we'll despair,"

would willingly be even in part responsible for the Can there really be any amongst our body who disaster detailed in the Mermaid, or think a few perce too much with which to purchase a share in the blessings which hundreds of grateful hearts may pour upon our lifeboat!

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 158s. 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 with a few kindred (but more practical) spirits. May discuss certain subjects appearing in the MECHANIC I ask if our mechanical friends at Derby could not attempt a branch?

[ocr errors]

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 many-enough, 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.

[graphic]
[ocr errors]
« ZurückWeiter »