The Velocity of Light 2 1 5 



had been told of their living in the condensing tank of a 

 steam engine in Lancashire where the temperature was 

 over 90 F. 



March lyth, 3O5th meeting. The news of the assassina- 

 tion of the Czar of Russia led to a conversation on explosives, 

 which was followed by one on the electric lighting of part 

 of the City of London. 



May igth, so/th meeting. Professor Stokes gave an 

 account of a paper on the " Velocity of Light," just read to 

 the Royal Society by Messrs. James Young and George 

 Forbes. 1 In their experiments they used, instead of the 

 single reflector employed by Cornu, two distant reflectors 

 of the light of the artificial star, so placed that, in the 

 observing telescope field two stars are at first seen, one being 

 3 miles, the other 3^ miles away, so that, on measuring the 

 velocity of the toothed wheel, the stars were eclipsed succes- 

 sively instead of simultaneously, the critical velocity being 

 that which made the two stars of equal brightness, not that 

 which, as in Fizeau's and Cornu's experiments, made them 

 vanish. Besides this a bluish light was observed when the 

 increasing speed of rotation brought a star near its position 

 of eclipse, and a reddish light when it had just passed this, 

 indicating that the blue light travels faster than the red in 

 air. It had been supposed that the differences in velocity, 

 inferred from astronomical phenomena, were due to ponder- 

 able matter in the air and that in vacuo both travelled alike, 

 but in these experiments there was a difference, though in 

 the contrary direction. This discovery leads to new ideas 

 of the luminiferous ether, with its apparently opposed pro- 

 perties of fluidity and solidity. 



Sir J. Hooker referred to the effect of the cold in 1879 on 

 the noted pine forest which fringes the eastern coast of 

 Italy for several miles from Ravenna southwards. In the 

 part recently visited by himself and Dr. Asa Gray every 

 pine tree, young or old, had been killed, and they were told 

 this was the case through the whole extent of the forest. 

 Other trees or shrubs growing with them, such as juniper 



1 Proc. R.S. vol. xxxii. page 247. 



