Photographs of Vibration Carves. 615 



observations were made from the moving train by projecting 

 a radium-tipped wire connected with the electroscope out of 

 the carriage window. When the steam from the engine 

 passed over the carriage, a very large positive charge was 

 shown by the electroscope. The potential gradient appeared 

 to be of the order of more than 1000 volts per metre, due to 

 the steam, as when that was blowm away from the carriage, 

 the potential fell to practically zero. 



On the southward journey, observations were taken at 

 most of the stopping-places, including the summit of the 

 Matoppo Hills. The electrification was always positive, no 

 abnormal values being observed. 



At the edge of the falls the potential gradient if it increased 

 at the same rate would have been enormous, but no doubt in 

 the cloud itself there w T ould be some conduction going on 

 (certainly convection). From the rate at which the elec- 

 troscope leaves diverged to a maximum, the charge at the 

 falls would be twenty-five times as great as that at a distance 

 of 1100 paces, viz. : 25,000 volts oer metre. 



The curve shows the rate up to within 500 paces. 



This of course is one day's observation ; no doubt the 

 potential gradient would vary from time to time. 





LXX. Photographs of Vibration Curves. 

 Bij C. V. Raman, M.A.* 



[Plate VI.] 



THE photographs of vibration-curves forwarded with this 

 note possess certain features of interest which seem to 

 justify- their publication. Experimental work on vibration- 

 curves relating to the sonometer, violin, and pianoforte that 

 has been published in recent issues of this Journal, con- 

 siderably interested me and induced me to undertake some 

 work in the same direction. 



The photographs (figs lto 9, PL VI.) were obtained, working 

 with an apparatus a description of which has already been 

 published elsewhere f. 



The idea of the construction of this apparatus was sug- 

 gested to me in 1908 by the problem of the motion of the 

 bridge of the violin. I recognized that the bridge is subject 

 to a normal forcing of double the frequency of the oscillation 



* Communicated by the Author. 



t See ' Nature,' Dec. 9, 1909, on " The Maintenance of Forced Oscilla- 

 tions of a New Type," and * The Journal of the Indian Mathematical 

 Club,' October 1909. 



