abstracts: technology 575 



deflections up to 600 M (MacMichael degrees). On adjusting the 

 speed of the instrument used in these tests, as directed by MacMichael, 

 it was found that a speed of 1 14 revolutions per minute was required to 

 give a deflection of 10 M with water at 20° C. One series of tests gave 

 for viscosities over 0.15 poise, the equation 



absolute viscosity in poises = /x = 0.0042 (M— 17) (i) 



while a second series with variable speed gave 



M = 1.95 ju w + 0.000833 7 n~ (2) 



where n is the speed in r. p. m., and 7 is the density in g/cm^. These 

 two equations are not exactly equivalent, the difference being at least 

 partly due to the fact that the torsion wire was removed and replaced 

 between the two series of tests. The method of fastening the wire in 

 the pendulum does not permit an accurate adjustment of its length. 

 For this and other reasons the above equations are not intended for 

 application to all instruments with medium-sized wires. Each instru- 

 ment should be calibrated by the operator with liquids of approximately 

 the same density as those to be tested. Water is objectionable on 

 account of its high density and the small deflection. The Bureau of 

 Standards is prepared to certify to the viscosity of calibrating liquids 

 having a viscosity not exceeding 20 poises. W. H. H. 



