Form of Monochord. 53 
and dividing by 360. The numbers of vibrations of the fol- 
lowing Tables were determined in the same way. 
Itis not possible to raise the tone of the siren to any extent, 
and thus to render visible the higher partial vibrations of the 
same thread. But for lecture-experiments it will always be 
sufiucient to show the law of overtones for the slower vibrations; 
and if it is desired to go further than in the experiments I have 
described, it is only necessary to replace the excentric wheel 
by an elliptical wheel, or by a toothed wheel exactly centred, 
with, say, four teeth, so that for the same velocity of rotation 
the number of shocks is doubled or increased fourfold. Ihave 
obtained the best results with toothed wheels of various forms, 
but think it more convenient so to choose the thread, its 
length and tension, that the excentric wheel suffices for the 
experiment. 
In order to demonstrate the Law of lengths, it is advisable 
to take a longer piece of a not too thin white silk thread, 
which will be nearly the same length for great differences of 
tension, and to stretch it over a measure and mark off equal 
distances with India ink. Thus, in the experiments to which 
Table II. relates, a thread of button-hole silk 2 metres long, 
and marked off into lengths of 10 centim., was attached: to the 
lever of the apparatus, so that the first mark fell at the point 
of attachment, passed over the pulley, and stretched with 
a force of 60 gr. by weighting the scale-pan with shot. 
Between the siren and the upright carrying the pulley-wheel 
I placed a table, carrying a small iron support with a clamp to 
grip the thread. In the Table, / denotes the length of the 
vibrating thread and N the number of oscillations for the 
fundamental note. 
TaBuE LI. 
N, N, 
é: N. Nn Z. N. Nn 
eee metre 
1:00 54:0 1 1:00 54:0 ] 
1:00 49:0 1:10 0:90 59°8 0:90 
1:20 45°1 1:18 0°80 67°8 0°79 
1°30 41:8 1529 0-70 17:3 0:70 
1:40. 38'4 128 0:60 90°7 0:59 
We have therefore N,: N,=/,:1,; the deviations from the 
law which the table shows are within the limits of experimental 
errors. 
Thirdly, in order to show that, with threads of the same 
