﻿A Wide Angle Lens for Cloud Recording. 999 



Z 

 With values of J greater than 30 the loss of energy in a 



collision is comparatively large, so that the velocity of agita- 

 tion is less than seven times W, and in these cases the formula 

 for W in terms of / and u is not so accurate as in the cases 



Z 



where - is less than 30 and u comparative^ large. 



P 



Z 



Table II. shows for the higher values of - that the mean 



° P 



free path increases with decrease of u, but for the lower 

 values it decreases with decrease of velocity of agitation. 

 In the other gases the mean free path increases for the 

 smaller values of the velocity of agitation. 



The values of X show that with this gas there is a 

 remarkable increase in the loss of energy of an electron in 

 a collision for comparatively small increases in the velocity 

 of agitation from the values 13 x 10 7 centimetres to 15 X 10 7 

 centimetres per second. 



Electrical Laboratory, Oxford, 

 July 1922. 



L XXXIX. A Wide Angle Lens for Cloud Recording. By 

 W.N. Bond, M.Sc.{Lond.), A.R.C.S., A.Inst.P., Lecturer 

 in Physics, University College, Reading*. 



[Plate VII.] 



THIS paper consists of a short description of a lens that 

 might be used for obtaining a photographic record of 

 the clouds visible at a meteorological station at definite 

 times, or for similar purposes, such as recording lightning 

 flashes. 



The special feature of the lens is that its field of view 

 embraces a complete hemisphere ; so that if the lens be 

 arranged to face vertically upwards, all the clouds visible 

 at the station at any one time can be recorded photo- 

 graphically on a single flat plate or film. The resultant 

 photograph (see PI. VII. J is circular, any clouds at the 

 zenith being reproduced in the centre of the circle, and any 

 near the horizon appearing near the edge of the circle. 

 Such apparatus might, of course, be used at two stations 

 simultaneously to obtain the altitudes of the clouds. 



* Couimutiieated by the Author. 



