ON THE MODULUS OK TOI;*H>\M. IMCIDITV OK MKTM. \VIKES. 



to the axis of the rod, which was then slit down to this point with a fine saw. A 

 very thin piece of metal was then inserted in the slit, the collar placed on and screwed 

 up tightly by the steel screw S, and a hole bored down the axis of the rod of the 

 same size as the wire to be used (No. 20, B.W.G.). In this way a 

 neat clamp is formed which grips the wire all around ite circumference 

 at a perfectly definite point, viz., the ends of the jaws. 



The lower end of the wire is held in a clamp exactly similar to 

 that at the top. This clamping rod has a screw thread at its lower 

 end by which the vibrator is fixed to it, l>eing screwed home against 

 a projecting flange. Below the screw thread, the rod was turned 

 down to ^ inch in diameter and one half cut away, so as to leave a 

 plane face for affixing the mirror used in timing the vibrations. This 

 mirror was held in a light brass frame which could be fixed in a \L 



perfectly definite position on the clamping rod hy means of two small 

 screws. 



The vibrating plate hangs alxnit 1 inch below the top of the box, 

 and above it a ring of gunmetal is supported on two horizontal glass 

 rods going from side to side. This ring is for determining the 

 moment of inertia of the vibrator, and can easily l>e lowered by hand p ig 2 



on to the plate. The plate is a circular disc of gunmetal f inch 

 thick and 5 inches in diameter. The outer edge of the upper face is turned down 

 about -^g inch. The ring exactly fits on to the groove so formed, and there is thus 

 no difficulty in placing it centrally on the plate. 



In order to set the plate in vibration without swinging it like a pendulum Ixib, the 

 following device was adopted. Two glass jets inclined at 45 degrees to the vertical in 

 opposite directions are fixed underneath the plate, and alxmt \ inch below it, one at 

 each end of a diameter. These two jets are connected together at the bottom of the 

 lx)x by a glass tube which passes out through the side, and is joined outside to 

 3 or 4 yards of tine " composition " tubing, which passes along the walls of the 

 laboratory and ends on a small table l>eside the olwerving telescope. Here it is joined 

 by means of a piece of indiarubber tubing to a small glass funnel, and by depressing 

 this in a dish of mercury a wind is sent through the jets which puts a couple on the 

 plate and rotates it. By properly timing the instants at which the funnel is lowered 

 into the mercury (by watching through the telescope), the amplitude of vibration of 

 the plate is quickly increased. 



The Heating Arrangements. 



Oleervations of the periods of vibration of the wires tested were made in general 

 at five temperatures. \i/.., at the temperature of the room, about 16 C., at 35 C., 

 55 C., 75 C., and 100 C.. and also in some cases at 126 C. These temperatures 



