The Velocity of Light. 67 



Mr. Griffith afterwards exhibited various spectra, including one 

 of human blood ; and made some remarks on Mr. Huggins' 

 method of determining the motions of some of the stars, by means 

 of the Spectroscope. 



Thursday, October 15th, 1868. 



The Fifty-first Meeting of the Society was held at the President's 

 House. 



Several rules were passed concerning the admission of Asso- 

 ciates. 



It was resolved " that efforts be made to enable the Society to 

 meet for the future in the Vaughan Library." In consequence, a 

 petition to the Headmaster requesting permission was signed. 



The exhibitions were : — 



Specimens of various kinds of Hornets . . . . By Balfottk. 



A collection of Shells from Algeria ; an instrument used by an Algerian 

 Chief for scratching his back . . . . . . By Evans. 



An egg of the great Bustard . . . . . . By Clarke. 



Some stellate cells imder the microscope . . By Bashfoed. 



Mr. Griffith exhibited Mr. De la Rue's new galvanic battery, and 

 two sextants ; one a box sextant, the other an instrument made 

 by Ramsden. 



The President exhibited some drawings of the late Solar Eclipse. 



Balfour then read the following paper on 



THE VELOCITY OF LIGHT.* 



The question of the velocity of light in vacuum is not in any 

 way affected by any theories as to what light is. It will be best, 

 however, to adopt the theory according to which light is due to 

 the undulations of a substance called ether, which is supposed to 

 pervade all space, — luminous bodies transmitting the vibrations 

 of their molecules to the ether in which they oscillate ; because, 



• This Paper is based principally on a Memoir of M. Delaunay. 



