106 



Anniversary Meeting. 



[Not. 30, 



the lenses being cemented, this object-glass will transmit an unusually large 

 portion of light. The respective indices of the glasses were determined by 

 making facets on their edges at an angle of 60°, and observing spectral 

 lines through the prisms thus formed with a spectroscope of such magni- 

 tude as to admit of their being placed on its table. The distinctness with 

 which even faint lines were seen through 12 inches of the glass is a most 

 satisfactory proof of its purity and clearness. From these Professor Stokes 

 computed the curves for the lenses ; and his numbers were almost identical 

 with those which Mr. Grubb had obtained. 



I may mention that some fears had been entertained that the equality of 

 curvature in the adjacent surfaces might call up a ghost, if the lenses were 

 used uncemented, and that this has been tried and no such effect was 

 visible. Subsequently a rather novel addition has been made, bearing 

 upon the radiation of heat from the stars. An object-glass intercepts so 

 much of the heat-rays that, to economize the infinitesimal effect which is 

 expected, a metallic mirror is more promising. The equatorial is there- 

 fore, at the suggestion of Mr. De La Rue, provided with the means of 

 changing the 15-inch achromatic for an 18-inch reflector; and this has 

 been accomplished by means notable for their facility and their safety. 



The instrument will be ready for trial in December of the present year. 

 In the meantime it may be said that the object-glass, notwithstanding the 

 difficulty of working one of so short a focus, gives promise of very high 

 excellence. 



With respect to the equatorial, it has been ascertained that a force of 

 2 lb. applied at the eyepiece is sufficient to move the telescope easily on its 

 declination axis, and 1^ ib. on its polar axis ; however, when all its parts 

 are put together, these forces may require to be increased ±. 



The anticipations which I ventured to express in may last year's Address, 

 of the renewal in the summer of the present year of the researches on the 

 temperature of the sea at great depths, and on the nature of the sea- 

 bottom and the life existing in its vicinity, have been realized by an ample 

 provision on the part of Her Majesty's Government, and a devotion on the 

 part of the Fellows of the Royal Society, viz. Dr. Carpenter, Prof. Wyville 

 Thomson, and Mr. Gwyn Jeffreys, meriting the highest praise. The ex- 

 istence of persistent deep-sea currents of very different temperatures in 

 proximity to each other, and their influence on the inhabiting forms of 

 life and on the nature of the sea- bed, together with the great extension of 

 our knowledge of the variety and characteristics of the new forms of life 

 which have been discovered, justify the belief that we have embarked on a 

 field of discovery and research which will not soon be exhausted, and which 

 will have no unimportant bearing on the earlier geology of our globe, as 

 well as on our knowledge of the life at present existing on the submerged 

 portions of its surface. 



It had long been inferred by naturalists that species of the marine 



