VOL. XXIII. No. 9.] 



POPULAR SCIEITCE NEWS. 



133 



Practical Cljenjistry aiid tlje 'fl.rts,. 



SOME CURIOUS TIME-KEEPERS. 



The engraving given below illustrates a 

 "puzzle-watch" constructed by an ingenious 

 Frenchman, M. Schwab, and described in 

 Z.a Nature. It is of the same class as the 

 clocks often seen in jewellers' windows, 

 which consist only of a glass dial and hands, 

 the machinery which moves them being con- 

 cealed in the hands themselves. This watch 

 is even more mysterious, as the hands are too 

 small to contain any hidden machinery, and 

 the dial being entirely of transparent glass, 

 there seems to be no possibility of any con- 

 nection with clockwork ; and yet the watch 

 goes and keeps good time. 



Fig. I. 



Fig. I. Viewofwatch. Fig. a. Detailsofconceiiled mechanism. 

 Fig. 3. Sectional view. C, C, outside protecting glasses; J, 

 dial-plate; D, space in which the hand.s revolve; E, II, G, 

 three wheels connecting the hour with the minute-hand; A, 

 glass wheel with metallic toothed edge transmitting the 

 movement of the clockwork to the hands; F, B.two plates of 

 glass 8upi>orting A and the other machinery. 



A study of the engraving will solve the 

 mystery. In Fig. i the watch, with its trans- 

 parent dial, is shown, and in Fig. 3 the clock- 

 work concealed in the metallic rim. In Fig. 

 3 a side view in section is given, from which 

 it will be seen that a wheel of transparent 

 glass., the periphery of which is provided 

 with a metallic gearing, serves to transmit 

 the motion to the hand.s. The minute-hand 

 is directly attached to it, and the slower 

 motion of the hour-hand obtained by small 

 gear wheels (Fig. 2) concealed by the orna- 

 mentation around the centre of the dial. 

 There are, in fact, six plates of glas.s compos- 

 ing the watch : the two outside ones for pro- 

 tection, the dial plate on which the figures 

 ate painted, and two other plates which support 

 the moving glass plate and the accessory 

 machinery. When in position in the watch 

 these different plates cannot be seen, and the 



source of the power which moves the hands 

 is completely concealed. 



As a practical use for a watch of this sort, 

 it has been suggested that it may be placed in 

 a magic lantern, and its image projected on a 

 screen in any suitable locality, thus taking the 

 place of the more expensive illuminated 

 clocks, and showing the time at all hours of 

 the night. 



Fig. z. 



A very simple, but tolerably accurate, sun- 

 dial is shown in Fig. 2, which is a representa- 

 tion of one made in England in the last century, 

 when they were quite commonly used in cer- 

 tain districts, in place of the more expensive 

 watches. It depends upon the varying height 

 of the sun above the horizon during the day, 

 and not upon its distance from the meridian, 

 as with an ordinary dial. It consists of three 

 rings, the inner one moving freely between 

 the two outer ones. On the outside rings are 

 engraved the initial letters of the months of 

 the year, and opposite these, on the inside, 

 are the hours of the morning and afternoon. 

 The movable ring is pierced with a small 

 hole. 



It is evident that if the opening in the 

 instrument is turned towards the sun at sun- 

 rise, a luminous spot will be thrown upon the 

 inside of the ring, and, as the sun mounts 

 higher in the sky, the spot will move down- 

 wards till noon, when it will turn and move 

 up again till sunset, and it is only necessary 

 to mark the hours where the light falls for a 

 single day to obtain a ready means of learning 

 the time, at least approximately ; but a cor- 

 rection is necessary for the varying height of 

 the sun at different seasons of the year, .so the 

 ring with the opening is made movable, and 

 once a month is moved so the opening comes 

 opposite the initial letter of that month. The 

 extreme error of this instrument is not 

 more than fifteen minutes, and it forms a very 

 cheap and useful substitute for a watch. | 



Fig. 3 shows a similar dial made out of' 

 pasteboard, which any one can copy who 

 takes an interest in the matter. A circular 

 box answers very well for the frame, and a 

 long slit is cut in the rim, corresponding to 

 the space between the initials of the months. 

 A band of heavy paper pierced with a small 

 hole answers for the movable ring, and 



is placed so as to cover the slit, and 

 moved backward and forward according to 

 the season of the year. The easiest way to 

 find the position of the letters and figures is 

 by comparison with a clock. A single day's 

 comparison will determine the position 01 

 the hour figures, and on the first of each 

 month the instrument may be set at noon, 

 and the initial letter of that month written in 

 the proper place. As it is highly important 

 that the instrument should be held perfectly 

 vertical while taking an observation, it is sus- 

 pended from a chain by which it is held in the 

 hand while it is turned so as to bring the 

 opening to face the sun, when the spot of 

 light falling inside the ring will indicate the 

 hour of the day. A small plumb-line may be 

 placed inside if preferred. 



In Fig. 2 the mathematical laws governing 

 the instrument are indicated, and it will be 

 seen that whatever may be the height of the 

 sun above the horizon at noon, with the vary- 

 ing seasons, the spot of light indicating the 

 hour will always fall upon the same place, 

 provided the opening is moved the proper 

 distance upon the outside of the ring. It will 

 be readily understood that the nearer one 

 approaches the equator, the more accurate 

 will be the indications of this instrument, for 

 there the elevation of the sun above the hori- 

 zon varies the most at different hours of the 

 day, while at the poles the variation is almost 

 imperceptible, and the "sun-dial" would 

 always indicate the same time. This in- 

 strument is a very curious and novel one, 

 and it is rather remarkable tliat this method 

 of determining the time has never come into 

 more extensive usdT 



NOVEL WOOD-JOINERY. 



The accompanying illustration shows some 

 curious ways in which two pieces of wood 



may be joined together. Apparently the 

 impossibility of separating them is onlj' 

 equalled by the mystery of how the}' were 



