Stevens — Method of Measuring Surface Tension. 245 



Art. XXIV. — A Method of Measuring Surface Tension; by 

 James S. Stevens. 



In the methods of measuring surface tension which have 

 formerly been employed there seems to be two difficulties : 

 the weights applied to break the tension cannot be added in 

 continuous increments, and they afford a certain accelerating 

 force beside their own mass when they are dropped on to a 

 scale pan ; and secondly, it is difficult to apply the pull 

 exactly at the center of inertia of the body used to break 

 through the surface skin. The second difficulty was overcome 

 in a method described by T. P. Hall, where filaments of glass 

 were detached from a liquid surface by weights applied to a 

 scale pan which formed the opposite end of a balance. 



A, hook gauge; BC, disk; D, sinker. 



The method described here is free from difficulties of the 

 above nature. An iron wire is bent into the form of a T (fig. 

 1) and the cross allowed to float on the surface of water. The 

 body of the T projects a little distance into the center of a 

 coil of copper wire through which a current may pass. The 

 part of the T forming the plunger is adjusted so that its weight 

 is nearly sufficient to break through the liquid surface. " A 

 slight pull towards the center of the coil due to the passage of 

 a current will then accomplish this. The system is raised and 

 lowered by a rack and pinion so that it may be placed on the 

 liquid surface as gently as possible. 



By means of a continuous resistance the current may be 

 applied in small increments, and the amount required to break 

 through read from an ammeter. When the current is applied 

 the plunger immediately moves to the center of the coil and 



