154 proceedings: philosophical society 



with a rough, spongy coating of gold, applied electrolytically. An 

 arrestment table, meshing with the scale-pan and raised or lowered 

 by a rack and pinion, allows the object to be put on or taken off from 

 the scale-pan with the least possible disturbance. A guard ring sur- 

 rounds the suspension-wire at the surface of the water to help main- 

 tain a uniform surface-tension on the wire. 



The 767th meeting was held on February 5, 1916, at the Cosmos 

 Club. President Briggs in the chair, 58 persons present. The min- 

 utes of the 766th meeting were read in abstract and approved. 



REGULAR PROGRAM 



Mr. E. C. Bingham presented by invitation a communication, illus- 

 trated by lantern slides, entitled, Plastic flow. (To be published in 

 a later number of this Jouivnal.) 



Mr. E. Buckingham then presented a paper entitled, Notes on the 

 theory of efflux viscosimeters. The paper was concerned with the rela- 

 tive determination of the viscosities of liquids, in terms of the viscosity 

 of some standard liquid, by the commonly used efflux method. In- 

 struments for making such comparisons must, in general, be standard- 

 ized, or have their "scales" determined, by means of a series of liquids 

 of which the relative viscosities have already been found by other 

 methods. The speaker's purpose was to show how the necessity for 

 such a standardization might be obviated and the series of standardiz- 

 ing liquids dispensed with. It was shown, by dimensional reasoning, 

 that whatever be the nature of the orifice or mouth-piece through which 

 the liquid is discharged, if the driving head be so adjusted that its 

 square root is proportional to the rate of discharge, the rate of discharge 

 will itself be proportional to the kinematic viscosity of the liquid. 

 Hence when this adjustment of the conditions has been effected, the 

 kinematic viscosities of two liquids are directly as their observed rates 

 of efflux. A viscosimeter which is so arranged that this adjustment 

 may be made need not be standardized at all, unless absolute values 

 are required; and in that event a single standard liquid of known 

 kinematic viscosity suffices. It was shown that if the viscosimeter is 

 a cylindrical burette with a small oriffice at the bottom, and if the ob- 

 servations consist in readings of the times at which the surface of the 

 liquid passes the marks on the burette as the liquid flows out at the 

 bottom, the inconvenient process of adjustment previously mentioned 

 may be dispensed with and the result obtained graphically. The 

 paper concluded with several suggestions regarding the practice of the 

 proposed method of viscosimetry. 



Discussion: Mr. Bauer asked what liquid would be best suited as 

 a standard. Mr. Abbot asked what degree of accuracy is practically 

 desired; if the accuracy wanted is high, is not the adhesion to the side 

 of the tube a difficulty? Mr. Buckingham stated that water would 

 be the best standard but that the practical requirements would make 

 necessary other intermediate standards as the viscosity increases. 



