ON GRAPHIC METHODS IN MECHANICAL SCIENCE. 



407 



The spot of light is used chiefly in meteorological instruments, as at 

 Kew Observatory. 



Fig. 33. 



-rrirT 



tWi--r- 



r^ 



TTi' 



Sir William Thomson's siphon-recorder was invented by him as the 

 outcome of his device for regulating the arrival of an electric impulse 

 through long submarine cables. It was used by Professors Jenkin and 

 Ewing ' in their experiments on the friction 

 between surfaces moving at low speeds. This 

 contrivance, a small, fine siphon glass, has its 

 shorter end dipped in aniline blue dissolved in 

 water, and the longer has its point bent so as 

 to stand almost touching the surface of the 

 paper. In order to make the ink run through, 

 so as to be deposited on the paper, it is con- 

 tinually maintained in a state of electrification ; 

 thus a continuous flow is obtained, forming a 

 fine line, without involving any friction. 



The kind of paper used for graphic records is a very important 

 matter, and Messrs. Bailey & Co., and others, have found it necessary, to 



' 'On Friction between Surfaces moving at Low Speeds,' by Fleeniing Jenkin, 

 F.K.S., and J. A. Ew ing. Philosophical Transactions of the Royal Society, vol. clxvu. 

 part. ii. 



