92 



Prof. Tyndall on a New Series of 



[Recess, 



scale. I cannot speak with exactness, as this part of the spectrum re- 

 quires remapping. 



I have evidence that the prominence was a very fine one. 



The instrument employed is the solar spectroscope, the funds for the 

 construction of which were supplied by the Government-Grant Committee. 

 It is to be regretted that its construction has been so long delayed. 



I have &c, 



J. Norman Lockyer. 



The Secretary of the Royal Society. 



IX. " On a New Series of Chemical Eeactions produced by Light." 

 By John Tyndall, LL.D., F.R.S., &c. Received October 24, 

 1868. 



I ask permission of the Royal Society to draw the attention of che- 

 mists to a form or method of experiment which, though obvious, is, I 

 am informed, unknown, and which, I doubt not, will in their hands 

 become a new experimental power. It consists in subjecting the vapours 

 of volatile liquids to the action of concentrated sunlight, or to the con- 

 centrated beam of the electric light. 



Action of the Electric Light. 

 A glass tube 2'8feet long and of 2*5 inches internal diameter, frequently 

 employed in my researches on radiant heat, was supported horizontally. At 

 one end of it was placed an electric lamp, the height and position of both 

 being so arranged that the axis of the glass tube and that of the parallel 

 beam issuing from the lamp were coincident. The tube in the first experi- 

 ments was closed by plates of rock-salt, and subsequently by plates of 

 glass. 



As on former occasions, for the sake of distinction, I will call this tube 

 the experimental tube. 



The experimental tube was connected with an air-pump, and also with a 

 series of drying and other tubes used for the purification of the air. 



A number of test-tubes (I suppose I have used fifty of them in all) were 

 converted into Woulfe's flasks. Each of them was stopped by a cork through 

 which passed two glass tubes : one of these tubes (a) ended immediately 

 below the cork, while the other (b) descended to the bottom of the flask, 

 being drawn out at its lower end to an orifice about - 03 of an inch in dia- 

 meter. It was found necessary to coat the cork carefully with cement. 



The little flask thus formed was partially filled with the liquid whose 

 vapour was to be examined ; it was then introduced into the path of the 

 purified current of air. 



The experimental tube being exhausted, and the cock which cut off the 

 supply of purified air being cautiously turned on, the air entered the flask 



