4 ON THE VISCOSITY OE INTERNAL FRICTION 



ao as to envelope the receiver, which then rested on the wooden support YY. 

 The tin vessel itself rested, by means of projections on the brackets QQ. The 

 outside of the tin vessel was then well wrapped up in blankets, and the top 

 the brass plate EE covered with a feather cushion; and cold water, hot 

 water, or steam was made to flow through the tin vessel till the thermometer T, 

 seen through the window \V, became stationary. 



The moveable parts of the apparatus consist of 



The suspension-piece a, fitting air-tight into the top of the tube and holding 

 the suspension-wire by a clip, represented in fig. 5. 



The axis cdek, suspended to the wire by another clip at C. 



The wire was a hard-drawn steel wire, one foot of which weighed 2'6 grains. 



The axis carries the plane mirror d, by which its angular position is observed 

 through the window C, and the three vibrating glass disks /, g, h, represented 

 in fig. 3. Each disk is 10'5G inches diameter and about '076 thick, and has 

 a hole in the centre '75 diameter. They are kept in position on the axis by 

 means of short tubes of accurately known length, which support them on the 

 axis and separate them from each other. 



The whole suspended system weighs three pounds avoirdupoise. 



In erecting the apparatus, the lower part of the axis ek is screwed off. 

 The fixed disks are then screwed on, with a vibrating disk lying between each. 

 Tubes of the proper lengths are then placed on the lower part of the axis 

 and between the disks. The axis is then passed up from below through the 

 disks and tubes, and is screwed to the upper part at e. The vibrating 

 disks are now hanging by the wire and in their proper places, and the fixed 

 disks are brought to their proper distances from them by means of the adjusting 

 nuts. 



ns is a small piece of magnetized steel wire attached to the axis. 



When it is desired to set the disks in motion, a battery of magnets is 

 placed under N, and so moved as to bring the initial arc of vibration to the 

 proper value. 



Fig. 4 is a brass ring whose moment of inertia is known. It is placed 

 centrically on the vibrating disk by means of three radial wires, which keep 

 it exactly in its place. 



Fig. 7 is a tube containing two nearly equal weights, which slide inside 

 it, and whose position can be read off by verniers. 



