466 



NATURE 



[February i, 1912 



a ring of the less d^nse liquid through the liquid of greater 

 density, but it Is not possible to project a vorfox ring of 

 the liquid of (jrf^atfr (lontiity through the liquid of Ifss 

 density. Thus n ring of lierosenc oil lan b** projprtwl 

 through wnur, Inil n ring of carb<in totrarhioride cannot. 

 Hy projecting ring-* of liquid paraffin through hot water, 



camera, and the double viewii which were obtaioMl, wh<>i 



examined, as they should N*, with n stereoscope, 

 mechanism of x\\r- rings in a much finer mann< 



Ix- obtained from single views. The electrical sp 



employed was very similar to the primary spark ir 

 the <!«»nding station for wireless telegraphy. Th«- - 



5 —stereoscopic view of two vortex rings produced Mmultaneously. 



and thence into :in underneath stratum of cold water, very 

 pretty solid rings of paraflin were obtained and preserved. 



The problem of photographing these rings was one of 

 peculiar ditliculty. The rapidity of their motions made it 

 necessary to nialve exposures which would be of the order 

 of only one twenly-tlve-thousandth of a second. Of course, 



optic device required that two sp...,.-. :., i>arated in >\>ii< 

 by a distance equivalent to that between the lenses of th- 

 stereoscopic camera, should be simultaneously produced. A 

 very special form of double spark-gap was constructed so 

 that the sparks took place between amalgamated zinc 

 terminals and the clean, bright surface of mercury. 



Fig. 6. — Stereoscopic view of two vortex rings uniiing. 



no mechanical shutter could be constructed to -i\ 



an exposure. An electric spark method, ;iii »p...... 



arrangement, and a timing device were finally devised 

 which gave excellent results and fully exposed plates. The 

 majority of the pictures were obtained with .t st( no-copic 



NO. 2205, VOL. 88] 



At iln^ moment when the rinj^ was photographed if 

 appi aied before the brilliantly illuminated surface of .i 

 plano-convex lens \i\ cm. in diameter. The ring as seen 

 in the camera thus appeared as a dark object against r< 

 brilliantly illuminated background. Ihe alternating 



