584 Prof. Kia-Lok Yen on the Coefficients of 



But if the suspended system has a moment of inertia I 

 and a period t, we also have the relation 



IV = A7r 2 I6/t\ 

 and therefore 



±7r 2 Wt 2 = ±TTl v [a 2 b 2 l(a 2 -b 2 )]w. 



Therefore 



_ 7rI0(a 2 -b 2 ) 



77 "" la 2 bH 2 w ' 



Thus we have an expression for the viscosity r\ in terms 

 each of which maybe made of such a magnitude that it may 

 be measured with the highest degree of precision. 



The Apparatus. 



The apparatus is the same one used by Harrington with 

 the suspension he designated as F in his report : this 

 suspension,, by the way, has been in use for a few years 

 now and has never been found to alter its zero position. 

 Fig. 1 shows the elevation of the apparatus. The outer 

 cylinder is geared to the chronograph drum K bv means 

 of a shaft running through the whole length of the steel 

 pipe Q, and thus the chronograph is employed as the 

 driving apparatus which causes the outer cylinder to 

 rotate and also as the recording device which registers 

 the speed of rotation The inner cylinder I is suspended 

 from the top of the tube T by means of an elastic steel 

 suspension S, so that the drag due to the viscosity of the 

 surrounding gas will cause it to deflect from its position of 

 rest when the outer cylinder is in rotation. A pair 

 of stationary cylinders (x, G are provided as guards for 

 the inner cylinder in order to eliminate the end effects. 

 The cylinders are supported by the heavy brass frame F, 

 which is mounted upon the thick steel plate P. The lower 

 end of the tube Q, together with the shaft and transmission 

 gears, is immersed in a cup C filled with mercury in 

 order to render the apparatus absolutely air-tight. The 

 whole of the apparatus is covered by a glass jar J and 

 sealed with mercury. A hole H is provided for letting in 

 or pumping out the gas the viscosity of which is to be 

 determined. 



The temperature inside of the apparatus is registered 

 by a Beckmann thermometer, calibrated with a standard 

 Baudin thermometer, and reading directly to 0*005 degree 

 centigrade. The room in which the determinations are 

 made is itself a constant temperature room. 



