228 THE FORMS OF CELLS [ch. 



a pair of metal rings, which happened to have a diameter of 

 71 millimetres; and, in a series of experiments, he set these rings 

 apart at distances of 55, 49, 47, 45, and 43 mm. successively. 

 In each case he began by bringing his oil-globule into a cylindrical 

 form, by sucking superfluous oil out of the drop until this result 

 was attained ; and always, for the reason with which we are now 

 acquainted, the cylindrical sides were associated with spherical 

 ends to the cylinder. On continuing to withdraw oil in the hope 

 of converting these spherical ends into planes, he found, naturally, 

 that the sides of the cylinder drew in to form a concave surface ; 

 but it was by no means easy to get the extremities actually plane : 

 and unless they were so, thus indicating that the surface-pressure 

 of the drop was nil, the curvature of the sides could not be that 

 of a catenoid. For in the first experiment, when the rings were 

 55 mm. apart, as soon as the convexity of the ends was to a certain 

 extent diminished, it spontaneously increased again ; and the 

 transverse constriction of the globule correspondingly deepened, 

 until at a certain point equilibrium set in anew. Indeed, the more 

 oil he removed, the more convex became the ends, until at last 

 the increasing transverse constriction led to the breaking of the- 

 oil-globule into two. In the third experiment, when the rings 

 were 47 mm. apart, it was easy to obtain end-surfaces that were 

 actually plane, and they remained so even though more oil was 

 withdrawn, the transverse constriction deepening accordingly. 

 Only after a considerable amount of oil had been sucked up did 

 the plane terminal surface become gradually convex, and presently 

 the narrow waist, narrowing more and more, broke across in the 

 usual way. Finally in the fifth experiment, where the rings were 

 still nearer together, it was again possible to bring the ends of the 

 oil-globule to a plane surface, as in the third and fourth experiments, 

 and to keep this surface plane in spite of some continued with- 

 drawal of oil. But very soon the ends became gradually concave, 

 and the concavity deepened as more and more oil was withdrawn, 

 until at a certain limit, th'e whole oil-globule broke up in general 

 disruption. 



We learn from this that the limiting size of the catenoid was 

 reached when the distance of the supporting rings was to their 

 diameter as 47 to 71, or, as nearly as possible, as two to three; 



