No. 1.-Simple Transit Instrument.

The object of the drawing Fig. 1, is to show the application of the common level, slightly altered, to the purposes of the transit instrument. My aim has been in this contrivance to enable any clock-maker to construct for himself an instrument by which he may ascertain the time for rating his clocks; not indeed with the accuracy attained by the usual transit instrument, but still with far greater accuracy than by the ordinary means of the dial and the meridian line. The instrument may be constructed at a trifling cost, and, as before stated, may be made to serve the purpose of a level (the spirit-level being added) when not in use as a transit.

The instrument is attached to a wall or side of a window, &c., situated as near as may be in the meridian of the place, by means of four screws, K K K, fig. 1, passing through the larger plate.

A second plate, having four adjusting screws and a stem, and containing the axis to which the frame of the telescope is fixed, is connected with the first plate by means of a simple loop of metal, a, fig 2, or a ball and socket, or Hook's joint. When the instrument is attached to the wall, the two adjusting screws, AA, are placed vertically by means of a fine plumb-line, and dots marked in their centres. The axis of the telescope (represented by dotted lines in fig. 2) is levelled by these two screws, the adjustment being made by means of a star or other object seen by direct vision and by reflection as usual. The two other screws, B B, serve to place the telescope in the meridian. The telescope is placed at right angles to

the axis by means of a fine plumb-line, suspended from the groove in the screw H, and passing over a corresponding groove in I, and this adjustment is made by the screws e c, the telescope being of course placed vertically, and the indications of the plumb-line observed during a revolution in the conical collars of the telescope frame. If required, of course the usual plumb-line apparatus could be attached. The revolution of the telescope in the collars furnishes the means of making the collimation adjustment, the wire plate being moveable for this purpose; it also allows of reversion during an observation; one of the conical rings turning in the collars is fixed to the tube, the other is moveable, and can be clamped by a screw, E. This moveable ring has upon it two marks at exactly opposite points, F F; a mark, f, is also made upon the frame in which the ring turns. When, therefore, the hairs have been made vertical, the mark F upon the ring is brought to coincide with f on the frame, and the ring then fixed by its screw E. The hairs will, therefore, be vertical when the second F is brought into the same position by a revolution of the telescope. The screws D D serve to clamp the telescope. The axis being conical (see fig. 2) can be tightened at any time by the insertion of a turn-key under the telescope, without altering the previous adjustments, and a divided circle might be attached to the stem Q, if required, for placing the telescope at any angle of elevation; or a common quadrant applied to the telescope for ordinary purposes. The construction of the telescope is of course the same as in other instruments in which cross hairs are employed. And in conclusion I may observe that every direction for placing a transit instrument in the meridian, will be found in the 2nd edition of Mr. Sims's admirable treatise on surveying instruments. I may state, also, that I have for some time used a telescope merely fixed to the frame c c (without the contrivance of the collars, &c.), for ascertaining the rate of watches, by the passage of the fixed stars across the wires, when I did not require the true time.

99

The sketch fig. 3 is the representation of a contrivance to enable a draughtsman to rule any number of equi-distant parallel lines, which are frequently required in mechanical and other drawings. It consists merely in the addition to the common parallel rule of an adjusting screw for limiting the distance between the lines, and a socket for holding the pen or pencil so as to enable the draughtsman to rule with greater accuracy than by hand alone. The rule, however, can be used with or without either of the additions, by withdrawing the adjusting screw, &c. The addition is made to the most common parallel rule, and also in the simplest way, so that the artist or engraver may be enabled to make it himself. For more accurate purposes the treble parallel rule would be preferable, and the socket containing the pencil, &c. should slide upon a raised plate of metal fixed along the edge of the rule, and perpendicular to its face; or the usual dividing point and frame might be adopted for short lines. It is evident that by having the edge of the rule indented, waving lines might be drawn.

Mode of using the Rule.-The method of using the instrument is to withdraw the adjusting screw, so that the rule shall open the required distance, press

the lower half of the rule firmly to the paper with two of the fingers, and the upper with the other fingers, apply the socket containing the pencil to the edge of the rule, elevate, or depress the pencil by means of the point at C till it touches the paper, and draw a line. Now, with the two fore-fingers slide the upper half of the rule on the paper till stopped by the screw, the other half being held down firmly by the other fingers, and repeat the process for the lower half till this is stopped by the upper, then draw a second line, and so on. If it be required to draw lines upon a copper plate, as in etching, it will be necessary to allow the rule to rest upon borders of card-board, or the like, elevated a little above the plate, both to prevent the rule from slipping and from injuring the plate.

The adjusting screw is tapped only into the pillar A, the other half of the screw is left plain and slides through B. The pillars are fixed into the rule by nuts counter-sunk in the under side of the rule, but not so tightly as to prevent the pillars from turning a little, in order that they may accommodate themselves to the different distances to which the blades of the rule may be opened.

The objections to this simple micrometer have been that it has not been easily applicable to the reflecting telescope, as in consequence of the eye-piece being made in one tube, there has been no means of changing the position of the micrometer; and also that the divisions of the micrometer, in its ordinary form, are distorted by the eye-glass. I have endeavoured to remove these objections thus ;-I have racked the tube which carries the diaphragm of the eyepiece, and applied an endless screw. By this means I can place the micrometer in any required position. second defect I have sought to lessen by giving to the pearl slip a curvature, whose radius is the focal distance of the eye-glass. The plate carrying the pearl slip is attached to the diaphragm tube

The

Fig. 4.

by two long screws, and by removing this plate, a circular pearl micrometer, or a plain diaphragm, may be substituted. Thus the same eye-piece becomes available for several purposes.

Fig. 4 represents the eye-piece. The endless screw is contained in the box A, and the dotted lines show the racking of the diaphragm tube, and the micrometer secured to its plate and curved by the two screws B B.

Fig. 5 represents the pearl slip, and its plate, removed from the eye-piece. B B are the two flat-headed screws which confine and give the requisite curvature to the micrometer; a a the two holes for the insertion of screws for the purpose of attaching it to the diaphragm

tube.

Your correspondent, Mr. Davy, sometime since, described what he considered to be the principle of the electrical telegraph exhibiting at Exeter Hall (see No. 758). I was induced to make a small model according to his plan, which I found fully to answer. Since then I have made the following alterations, by which nine letters may be shown with only one needle and one coil. The top of the box, in which the needle, &c. are enclosed, is pierced with three sets of three holes each, and numbered 1, 2, 3, as in figure 6. Below this is the needle carrying a disc pierced with three holes, which correspond with one row of the aperture above, viz. 1, 2, 3. Under the needle is another disc, havI. G. H.

Now, when the needle is in one position, say its ordinary one, the letters A. D. G. will appear, with polarity in the coil, C. F. I., &c. By this construction, therefore, a saving may be effected in coils, needles, &c., though a coil and needle will be required for intimating to the person who is to read the words, what compartment he is to look at for the several letters; some loss of time will also be occasioned. My object, however, in contriving this, has been to make it an amusing experiment for a class. It may, perhaps, afford a hint which may be applied to more important purposes. Other sets of letters could be added at different parts of the discs if required.

Fig. 6 represents the top of the model of the electrical telegraph, with the sets of apertures I. II. III.

Fig. 7, the disc, which is fixed to the needle with its apertures.

Fig. 8, the disc beneath the needle, &c. upon which are the letters.

101

much expectation that I should obtain the 2007., but for a love of mechanics, blended with the hope of being useful to the public) and devised a plan of which the following is a description:

The machine consists of a rod composed of a number of lengths, formed of strips of whalebone or cane bound together. The brushes and scrapers are fixed at right angles to the top of this rod, and the handles of them are elastic, in order that they may contract or extend, according to the size of the chimney they are used in. Beyond these brushes and scrapers, and forming a continuation of the principal rod, I place what I call a guide-rod, which is about 10 feet long, made tapering to the end, like, and of the same materials as, a fishing-rod. On the top of this guide-rod there is a ball, to prevent any rough places or defects in the chimney stopping its passage upwards. The purpose of this guide-rod is, that when it comes to a sharp angle in a chimney, it may bend up, and guide the brushes and principal rod round the corner.

Should

it bend the wrong way, if the sweeper twists the machine, it will right itself.

I leave you herewith a model, for your own inspection and satisfaction; and perhaps you will allow any of your readers who may desire so to do, to examine it.

I am, Sir, your

May 22, 1838.

THE CORNHILL

obedient servant, JOSEPH WALKER.

CLOCK-ANOTHER

METHOD OF PRODUCING MOTION WITHOUT APPARENT MECHANISM. Sir,-There have been two or three attempts described in the Mechanics' Magazine to account for the manner in which motion is communicated to the index of the clock now exhibiting in Savory's shop at Cornhill. I have not, myself, seen the clock, but I can hardly imagine that any of the expedients described by your correspondents, can be that which is resorted to; setting aside their clumsiness, they all require the revolution of a large circle, unsupported by a central axis, which, in practice, would necessarily involve immense friction and require great power. In my opinion, a much more feasible plan might be modified from the acknowledged contrivance of the dial exhibited in the Polytechnic Institution, although its particular application, the

displayed, is clumsy and objectionable.

Where the works of a watch are concealed in the feather part of an arrow, not only is a great counter-balancing weight rendered necessary at the pointed end, but also, a connecting bar, or shaft, to transfer the motion to the centre. The following plan appears to me to be an obvious improvement, and quite capable of producing all that is attributed. to Savory's clock, at least so far as the drawing in front of No. 795, Mechanics' Magazine, represents it:

Take a small Geneva watch, (of which there are several scarcely bigger than a shilling,) divest it of its outer casing, dial, pendant, and hands, and let the place of the pendant be supplied by the shaft and point of an arrow, proportioned to the size of the dial to be used, and let the feather part be affixed diametrically opposite-it will then present the annexed appearance in which the watch is at a.

a

Next, let a brass pipe which tightly fits on the hour-hand arbor of the watch, be cemented into the centre of the glass dial, so as to be flush with its surface. If then the hour-hand arbor be inserted into the cemented pipe, the index will move round the dial once in twelve hours, correctly indicating the time. To wind up, the index may be unfixed, if, as is usually the case, the winding arbor be on the face. There need then be no appearance of works or machinery to betray the contrivance, and the only weight necessary being in the centre, and equally distributed, the index might be as light and delicate as could be desired.

It is evident that there would be no difficulty in affixing a light index at the back of the transparent dial, by means of a central pipe, squared internally, to fit the minute-hand arbor of the watch, and long enough to pass through the cemented pipe and dial; reaching to the minute-hand arbor, and affixing thereon. There would then be two indices, as in an ordinary clock, one for hours, and the other for minutes; thus rendering exhibition much more wonderful and useful than Savory's.

Nov. 12, 1838.

NAUTILUS.

POSTSCRIPT, ON KINCLAVEN'S REPLY

TO NAUTILUS.

I perceive by your last Number that Kinclaven has shaken off his "long indisposition" (to attempt a reply, ne c'est pas?). He labours hard again to invest the question in the mist, which it was the object of my communication of last June (No. 773) to dispel; he does not make even an attempt to disprove either of the two simple positions on which the truth or falsehood of my proposition entirely hinges, (all the rest of my letter being merely a plain statement of undisputed facts) mamely

Firstly, ab: T:t; and, secondly, 360-a 360-b

if so,

360

t

=

(360

In the first page of his letter he writes thus:-"I repeat that there is not a single known case in the solar system where an equality exists between the astronomical expressions

PP

P-p

and Tt ;" but, on the succeeding page he T-t says "there is an equality between the P P Tt " "I allow and expressions P-p T-t'

it to be true."-(vide pp. 83-84, No. 796.)

This is only a small spice of the mess into which he is floundering, but as he promises a further communication, it would be a pity to spoil sport by interrupting him, until he has got over head and ears. I hope, however, that when he is convinced of his error, he will not again (as at page 245, vol. 27) limp off by saying it is “not necessary" that two persons should agree about a simple matter of fact.

NAUTILUS.

METHOD OF FINDING THE CURVES OF THE TEETH OF WHEELS FOR MILLWORK.

Sir, For the purpose of giving a general explanation of the method, a particular case of which was described in No. 752, let it be required to find the form of the curved part of the tooth of a spur-wheel, A, of any diameter, which is to work with another wheel, B, of any diameter, either greater, equal to, or less