492 Prof. W. A. Osborne and Mr. W. Sutherland. [July 5, 



250| 1 1 1 1 1 1 1 1 1 1 1 



O -2 4 -6 -8 I 1-2 1-4 1-6 1-8 Z 2-2 



Reciprocal of r-a. 



Fig. 6. 



As another instance of the applicability of this equation to a balloon, the 

 deflation values already given in fig. 3 may be cited. Calculation by the 

 three-point method gives here a — 2 - 03, b — 263. 



Conclusive as these values are that the rubber balloon, when initial 

 rigidity is removed, follows the equation (?• — a) (p—b) = c, it will be at 

 once obvious, from the values of a and b found here, that this is certainly 

 not the behaviour of a perfectly elastic substance giving equation (2). For 

 one thing, the value for a is far removed from zero and is suggestively close 

 to that of the initial radius in the two cases investigated. I abandoned the 

 theoretical analysis of my results at this stage, and handed over my data on 

 balloons and on bladders to Mr. William Sutherland, who has kindly 

 complied with my request to comment upon them (see p. 497 below). 



Rubber Balloons at the Elastic Limit. 

 In the course of this research a curious result was obtained with every 

 balloon which I inflated beyond the elastic limit. I invariably found that, 

 before the balloon burst, the pressure, over a considerable range, was a linear 

 function of the volume. Of the many instances obtained I will pick out two, 

 one giving a close approximation to a straight line on plotting volume against 

 pressure (fig. 7). 



One of the more divergent types is that given in fig. 8, which is a 

 continuation of the same experiment as fig. 2. 



As a rule, the straight line rises abruptly, producing discontinuity in the 

 graph. 



