932 
Proceedings of the Royal Society 
It is obviously unsafe to generalise from such a small number 
of observations, but the results brought out by the discussion of 
the figures may be stated as at least probably true : — 
(1) During daylight the air was always at a higher temperature 
than the water, but after sunset the water was warmer than 
the air ; and taking an average for the whole period, the 
mean temperature of the air was the higher. 
(2) The surface temperature followed that of the air, and was 
little affected by tidal changes. 
(3) The bottom temperature followed that of the air, but the 
crest of the heat wave was retarded by several hours, and 
the curve was profoundly modified by the tides. 
(4) The temperature was .higher at the surface than at the 
bottom during the day ; but, as a rule, it was higher at the 
bottom than at the surface by night. 
(5) When the tide flowed in the early morning it exercised a 
cooling effect on the bottom thermometers, but when it 
flowed at other times it produced a warming effect. 
The variations of temperature when the tidal effect is eliminated 
may be accounted for by the direct action of sun heat and radia- 
tion, propagated by conduction and convection beneath the surface. 
It is possible that when the tide enters the quarry after the sand 
over which it must flow to reach the entrance has been exposed 
for several hours to strong sun-heat, the water may be warmed by 
contact with it, and so exert a heating effect. On the other hand, 
when the sand has been uncovered by night, chiUed by radiation, 
it may cool the water passing over it, or at least not raise its 
temperature. This hypothesis explains all the phenomena which we 
have observed as yet, and is supported by a considerable number of 
experiments; but Mr Peddie and I are about to commence a critical 
research to test its applicability, and also to investigate the varia- 
tions produced by the currents in the quarry, the direction of the 
wind, and other causes. 
I have to thank Mr Peddie, Mr H. ^N”. Dickson, and Mr Lindsay 
of the University Physical Laboratory, Mr T. Morton Eitchie, 
B.Sc., Mr H. J. Gifford, and Mr W. A. P. Tait, for their valuable 
and self-denying assistance in making the serial observations 
described in this paper. 
