518 REPOET — 1886. 



the validity of the first argument, and have endeavoured to show that there are 

 elements of uncertainty surrounding the second ; nevertheless they undoubtedly 

 constitute a contribution of the first importance to physical geology. Whilst, then, 

 we may protest against the precision with which Professor Tait seeks to deduce 

 results from them, we are fully justified in following Sir William Thomson, who 

 says that ' the existing state of things on the earth, life on the earth, all geological 

 history showing continuity of life, must be limited within some such period of past 

 time as 100,000,000 years.' 



If I have carried you with me in this survey of theories bearing on geological 

 time, you will agTee that something has been acquired to our knowledge of the 

 past, but that much more remains still to be determined. 



Although speculations as to the future course of science are usually of little- 

 avail, yet it seems as likely that meteorology and geology will pass the word of 

 command to cosmical physics as the converse. 



At present our knowledge of a definite limit to geological time has so little 

 precision that we should do wrong to summarily reject any theories which appear 

 to demand longer periods of time than those which now appear allowable. 



In each branch of science hypothesis forms the nucleus for the aggregation of 

 observation, and as long as facts are assimilated and co-ordinated we ought to 

 follow our theory. Thus even if there be some inconsistencies with a neighbouring 

 science we may be justified in still holding to a theory, in the hope that further 

 knowledge may enable us to remove the difficulties. There is no criterion as to 

 what degree of inconsistency should compel us to give up a theory, and it should 

 be borne in mind that many views have been utterly condemned when later 

 knowledge has only shown us that we were in them only seeing the truth from 

 another side. 



The following Papers and Report were read : — 



1. Communication from the Grenada Eclipse Expedition. 

 By Donald MacAlistee, M.A., M.D., B.8c. 



2. First Eeport on our Experimental Knowledge of the Properties of Matter^ 

 By P. T. Main, M.A.—See Reports, p. 100. 



3. On the Critical Mean Curvature of Liquid Surfaces of Revolution. 

 By Professor A. W. RiJCKER, M.A., F.B.8. 



Let a mass of liquid or a liquid film be attached to two equal circular rings,, 

 the planes of which are perpendicular to the line joining their centres. 



It will form a surface of revolution, the equation of which is, according to Beer, 



y^ = a^ cos^ ^ + 13' sin' (p, 

 X =aE + i3F, 



where F and E are elliptic integrals of the first and second kinds respectively, the 



amplitude being ^, and the modulus k= \/a'--/3^/a = siu 6. 



If 6 be conceived as increasing from 0, when it is in the first quadrant the 

 figure will be an unduloid lying between the cylinder and the sphere, in the second 

 quadrant a nodoid, the limits of which are the sphere and a circle. In the third 

 and fourth quadrants the figure will be dice-box-shaped with a contraction in the 

 middle, being a nodoid in the third and an unduloid in the fourth quadrant. The 

 one passes into the other through the catenoid. 



If DOW we suppose the rings to be at a fixed distance apart and the volume of 

 the surface to be altered, the curvature will change, and the direction of the change 

 will depend on the diameter and distance apart of the rings, and on the magnitude 

 of the maximum or minimum ordinate (the principal ordinate), which lies halfway 



