Proceedings. 171 



In the discussion which followed this paper, Professor 

 Lamb, F.R.S., suggested that the phenomena could 

 probably all be interpreted on the basis of the general 

 theory of forced oscillations, combined with the fact, 

 pointed out long ago by Sir G. Stokes, that the surface of 

 separation of two liquids of slightly different densities has 

 greater inertia and less stability than a free surface of similar 

 extent, so that the natural periods of oscillation are com- 

 paratively long. According to the calculation of Stokes 

 (Camb. Trans.,\o\. 8, 1847), the superposition of a liquid of 

 density p on one of density p will diminish the speed 

 of the oscillations of the common surface in the 

 ratio */{(p — p')/(p + p')}- F° r example, in the case of oil of 

 density - 8, over water, the free oscillations will be three 

 times as slow as in the case of an air-water surface. 



{Microscopical and Natural History Section.] 



Ordinary Meeting, March 18th, 1895. 



JOHN BOYD, Esq., President of the Section, in the Chair. 



Mr. Mark Stirrup, F.G.S., read a paper describing 

 the geology of the Island of Barbadoes, and with Mr. 

 R. E. CUNLIFFE exhibited under the miscroscope slides 

 of the well-known Barbadoes earth containing siliceous 

 organisms. 



Mr. Oldham exhibited and described two new species 

 of fresh-water shells, Pisidium cruciatum and P. punctatum, 

 illustrated in the Nautilus, a monthly magazine published 

 in Philadelphia (Vol. viii., No. 9, 1895), and another, not 

 yet described, from New Philadelphia, Ohio. 



Mr. COWARD exhibited two skulls, stone weapons, and 

 hardened wood club, from Islands in the Pacific. 



M 



