March 24, 1882.] 



♦ KNOWLEDGE • 



455 



floor around. Again, the disastrous senselessness of " Parisian " 

 shoes, high-heeled and taper-toed, needs no enforcing ; but the 

 fashion which insists on them will need a very strenuous and deter- 

 mined opposition ere it is finally conquered. 



We are glad to be able to offer Mr. Treves our hearty congratu- 

 lations, both on the admirable lecture he delivered, and on the un- 

 mistakable success with which it has been attended. — Medical 

 Press and Circular. 



COMPOUND PENDULUM. 



AQCESTJOX was asked lately in K.nohledgk about the curves 

 drawn by the Compound Pendulum. I have made for myself 

 one of these instruments, by which were di-awn the curves which 

 I enclose. The machine was made as follows : — 



I procured two hollow brass rods about 3 ft. long. At 6 in. 

 from the top of each a steel pin 2 in. long is driven through, and 

 filed on the under side to a knife edge, to form the fulcrum for the 

 pendulum. A plug of ivory is ti.xed in the top of each rod, having 

 a small conical cavity drilled in it. On each rod are two cylindrical 

 leaden weights, which slide upon it, and can be fixed at any height 



spirit-level, and the arms which carry tlie pen horizontal. The 

 Pendulums are held up by strings towards a point under the centre, 

 and started by a trigger, by which they can be released, either 

 simultaneously, which gives a pointed curve, or one Pendulum at 

 any fraction of a swing before the other, by which a continuous or 

 looped curve is produced. This would be better done by an electro- 

 magnet, which 1 puri)0sc to try. I send a set of the curves repre- 

 senting the intervals of the musical scale, which are as follows : — 



That is, if one Pendulum vibrates 9 times while the other vibrates 

 8, they will draw a curve similar to that which can be produced 

 optically by the vibration of two tuning-forks, whoso vibrations have 

 the same ratio, J, which in music is called a Second. Equal vibra- 

 tions give Unison, a curve varying from a straight line to an ellipse 

 and a circle. If one vibrates twice as fast as the other, for which 

 it must be j of its length, an octavo is dra^vn, and so for the other 

 curves, according to the above ratios. 



Fig. 1. — Pendulum. 



(i of real Size.) 



by a collar and screw. Each weight is divided, because it is better 

 sometimes to nse half the weight on eah rod. (See Fig. 1.) Fig. 2 

 shows the top of the table. A and B are two pieces of mahogany, 

 1 ft. by 2 in., and 1 in. thick, morticed together at right angles, and 

 Screwed to the top of a tripod stand, C. Into the end of each are 

 fixed two brass screws, having a circular groove turned round their 

 necks, forming the notch in which the knife edges of the Pendu- 

 lams swing, and by turning the screws, the distance from the centre 

 can bo adjusted. On the top of this is &Ked a small box, 9 in. by 

 B in., and 34 in. high, so that its centre is just over the point where 

 the arms join. This box forms the table on which the paper is 

 laid, held down by springs. The pen is carried by two arms of thin 

 mahogany, jointed by a metal tube fixed tightly in the end of one, 

 the other working round it. Tlie pen is fixed in this tube. I use a 

 goose quill. I have tried glass tubes, but they are difficult to make 

 aud soon get clogged. Enough ink is held in the pen by a tongue 

 of quill inside it, almost touching the point. In each arm, at the 

 same distance, are the Pendulums, and from the centre of the table 

 fa a small screw filed to a sharp point, which works in the 

 conical hole in the top uf each pendulum rod. Thus there is very 

 Httle friction, except that of the pen on the paper, which can be 

 regulated by balance-weights. The table must be levelled by a 



Fig. 2.— Top of Table 



There are other intermediate interval.s, the curves of some of 

 which I have obtained. One of the rods must be jointed, so that 

 the lower half can be removed, in order to produce the higher ratios 

 of vibration. I shall be glad to give an account of all the different 

 curves, and the way of drawing the various forms of each, if you 

 think it would interest any of your readers. A description of the 

 curves, and the mathematical and musical principles involved, is 

 given in Deschanel's " Natural Philosophy," Part I, page 848, in 

 Jamin's " Conrs de Physique," vol. ii., p. 608, and in Ganot'a 

 " Physics," p. 207, with illustrations of Lissajou's experiment for 

 showing the curves optically by tuning-forks furnished with small 

 miiTors and vibrating at right-angles; but I have not found any 

 account of llie jnethod of drawing the curves by the Compound 

 Pendulum. E. LuxMOOKE. 



Health of Nasties. — An experience of twenty years as a 

 medical man in India, enables me to inform " F. C. S." that betel 

 chewing certainly does not prevent the natives from suffering 

 severely from malarious intermittent and remittent fevers. It is an 

 abominable habit — the lime used destroying the gums and teeth, 

 though it, of course, supplies some want to the system, as tobacco- 

 smoking dws.— B. M., F.R.C.S. 



