66 
DR. S. CHAPMAN ON THE SOLAR AND LUNAR 
As the heating of any volume element proceeds continuously for twelve hours, the 
total thermal energy communicated during the da)dight hours (and lost during the 
night time) is 
(91) 27 . HU 13 . 43,200 = 1*2 . 10" 8 . 
This refers to one square centimetre of the conducting layer of thickness e, and it 
may be noticed that the calculation is independent of e and of the situation of 
the layer. 
The pressure variation produced by this temperature change is much more 
uncertain, since the heating effect depends greatly on the density of the atmosphere 
of the conducting layer; also the variation of pressure will be less than that 
calculated from the equation dpfp = 0T/T, on account of the yielding of the adjacent 
atmospheric layers. If we suppose that the conducting layer lies between 90 and 
140 km. above the earth’s surface, its mass per square centimetre column is 
(92) 760.2.10~ 6 . 13'6 gm., 
13'6 being the density of mercury, and the difference of the pressures at top and 
bottom being approximately 2 . 10~ 6 atmosphere. The specific heat of air at the 
temperature of the atmosphere is about 0'24 (at constant pressure), while that of 
hydrogen is about 3*4. For the purpose of an approximate calculation we may take 
the specific heat as unity. In this case the total rise of temperature which would be 
produced by the amount of heat (91), in the above mass of gas, provided there were 
no loss, would be 
6 . 10“ 6 
in degrees centigrade. Hence dpfp, which must be less than 3T/T, cannot be 
so great as 3. 10 -8 . This is negligible compared with the estimated amplitude 
of the pressure variation due to the atmospheric oscillation Q 2 2 , which in the 
upper air is approximately 1/760 or 1‘3 . 10 -3 (assuming a surface amplitude of two 
millimetres of mercury, and a reduction in dpfp of about one-half, in the conducting 
layer, § 24). 
In order that the pressure variation due to the electric heating of the conducting 
layer might be comparable with that due to the main atmospheric oscillation Q 3 2 , 
the pressure of the region in which the conducting layer is situated would have to be 
of the order 10~ 10 atmosphere. Assuming the existence of the hydrogen layers 
mentioned in §21, this pressure would be attained only at a height of more than 
800 km. The pressure is of the order required for the ionisation of the conducting 
layer by ultra-violet radiation, according to Swann’s calculation ; but it seems more 
probable that the conducting layer is at a lower level. 
