1897.] Mr Baker, On the lines of striction of a hyperboloid. 333 



On the lines of striction of a hyperboloid. By Mr H. F. Baker. 



It was a known fact that the lines of striction of a hyper- 

 boloid formed two unicursal quartic curves. The most commonly 

 given equation shewed that the curve was an octavic curve with 

 six double points ; such a curve on a surface of the second order 

 could not be a proper octavic curve ; for a cubic surface drawn 

 through the double points and thirteen arbitrary points of the 

 curve would otherwise cut the curve in 12 + 13 = 25 points. The 

 question considered was what are the possible forms of such 

 octavic curves. 



(5) On the Action of Uranium rays on the Condensation of 

 Water Vapour. By C. T. R. Wilson, M.A., of Sidney Sussex 

 College, Clerk Maxwell Student. 



I have already (Proc. Roy. Soc, Vol. 59, p. 338, 1896 ; Phil. 

 Trans. A. 189, p. 265, 1897) described experiments upon the 

 effect of Rontgen rays on the condensation of water vapour. These 

 experiments proved that the rays, in traversing moist air, in- 

 troduce nuclei capable of acting as centres of condensation when 

 supersaturation exceeding a definite limit is brought about by 

 the sudden expansion of the gas. Nuclei, requiring exactly the 

 same degree of supersaturation to enable condensation to take 

 place upon them, are always present in very small numbers even 

 without the action of the X-rays ; but these rays enormously 

 increase their number. To produce the degree of supersaturation 

 necessary to bring these nuclei into play in air originally satu- 

 rated, a sudden expansion is necessary such that v 2 /v lf the ratio 

 of the final to the initial volume, exceeds 1*25 ; corresponding 

 approximately to a fourfold supersaturation. 



In the absence of X-rays and other disturbing influences, no 

 condensation is observed (after the removal of all foreign nuclei) 

 if v 2 /v 1 is less than 1*252. If v. 2 \v x lies anywhere between this 

 and 1*37 a rainlike condensation results, the drops being few 

 and scattered. Beyond this second limit dense fogs appear. 



The action of the X-rays is simply to increase the number 

 of the drops which are formed when v 2 /v 1 lies between these limits ; 

 the minimum expansion required for condensation not being 

 sensibly altered. 



The experiments described in the present paper show that 

 nuclei of exactly the same nature are produced in moist air under 

 the action of the Uranium radiation discovered by Becquerel. 



The form of apparatus used is represented in the accompanying 

 figure. 



