﻿920 Mr. A. H. Davis on Natural 



physiological basis of the seneation of light, and in the, 

 quality of the impulse the physiological basis of the sensation, 

 of colour. But though the impulses vary according to the 

 wave-length of the light causing them, the retino-cerebral 

 apparatus is not able to distinguish between the character of ; 

 adjacent stimuli, not being sufficiently developed for the 

 purpose. At most seven distinct colours are seen, whilst 

 others see, in proportion to the development of their colour- 

 perceiving centres, six, five, four, three, two, or none. This 

 causes colour-blindness, the person seeing only two or three 

 colours instead of the normal six, putting colours together 

 as alike which are seen by the normal-sighted to be different. 

 In the degree of colour-blindness just preceding total, only 

 the colours at the extremes of the spectrum are recognized 

 as different, the remainder of the spectrum appearing grey. 



LXXIX. Natural Connective Cooling in Fluids. 

 By A. H. Davis, M.Sc* 



[From the National Physical Laboratory.] 



Contents. 



Introduction. 



I. Theoretical. 



II. Experimental. 



Formulae. 



Apparatus. 



Experimental Observations. 

 Results. 



(a) Representation in the form ~H./k=~F(c 2 gd 3 aO/k 2 ). 



(b) Representation in the form H/k = ~F(d 3 0gac/kv). 

 Cooling Power of Fluids. 



Introduction. 



BY general reasoning from the principle of similitude!, 

 introducing certain plausible assumptions, it is possible 

 to obtain the following formula to represent the heat loss by 

 natural convection from similar bodies similarly immersed 

 in viscous fluids. 



liLlk0 = F(c 2 gL*ad/k 2 )f(cv/k), . . . (1) 



* Communicated by the Author, 

 f Davis, Phil. Mag. xl. p. 692 (1920). 



