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LVIII. An Absolute Determination of the Coefficients of 

 Viscosity of Hydrogen, Nitrogen, and Oxygen. By 

 Kia-Lok Yen, Ph.D., Research Assistant in Physics, 

 University of Chicago, recently appointed Professor of 

 Physics, Government University, Peking, China*. 



[Plate VIII] 



A LTHOUGH historical]}^ several methods have been 

 jTjL employed in the determination of the viscosity of 

 gases, practically all of the most careful measurements 

 have heretofore been accomplished with the transpiration 

 method. But, since it is an impossibility to obtain capil- 

 laries of uniform bore and next to impossible to accurately 

 determine the size and shape of the bore when it is not 

 uniform, and since there is always a possibility of the 

 formation of eddies at the ends of the capillaries and a 

 consequent distortion in the lines of flow of the transpiring 

 gas, the transpiration method is neither mathematically 

 rigorous nor experimentally exact, and so even the most 

 careful and accurate determination is but relative. It was 

 not until the development of that most accurate method 

 for the determination of the elementary electrical charge, 

 the "oil drop" method, the accuracy of which is limited 

 only by the accuracy in the measurement of the absolute 

 value of the coefficient of viscosity of the gas in which 

 the droplets fall, that there was created a demand for the 

 most accurate determination possible of the absolute value 

 of the coefficient of viscosity of gases. 



In order to meet this demand there has been developed, 

 bv Professor Millikan and his pupils, in the Eyerson 

 Laboratory, University of Chicago, a constant deflexion 

 apparatus the behaviour of which has proved most con- 

 sistent and the results of which can lay claim to accuracy 

 of a much higher degree than has ever been achieved bv 

 any other method -j\ 



As the viscosity of air determined by means of this 

 apparatus came out somewhat lower than the values usually 

 assigned to that coefficient %, the desirability of the redeter- 

 mination of the viscosities of other gases was at once 

 api arent ; and the work herein described is but a fulfilment 

 of a small part of a general plan to revise the whole of the 



* Communicated by Prof. K. A. Millikan. 



t See Gilchrist, Phys. Review, n. s. vol. i. No. 2, Feb. 1913, pp. 124- 

 140 ; also Bairington, ibid. vol. viii. No. 6, Dec. 1916, pp. 738-751. 

 | See Gilchrist and Harrington, ioc. cit. 



