250 Mr Blackadder on circumstances connected with the 
so different in their condition, yet not altogether disconnectea 
and which impinge on the opposite sides of the window, the con- 
densation of the moisture, and the forms which it is sometimes 
found to exhibit, will not be found inexplicable, without having 
recourse to any thing of the nature of radiation. If the cause 
of the absence of moisture on certain spots of the glass, (such as 
are to be seen, PI. IX. Fig. IV., on the middle and lower pane of 
the upper sash of the window), be not always very apparent, still 
the difficulty cannot be removed by supposing the influence of 
radiation. Unless, indeed, we are satisfied with saying, that 
some spots of the glass radiated their heat less copiously, or re- 
tained more of that which was radiated to them, than the other 
parts. This would be a very convenient mode of accounting for 
physical phenomena ; for, in adopting it, we would but rarely 
meet with any very imposing difficulties. 
Mr Murray has recorded * an observation made by him when 
travelling in a coach in Italy, and which he considered inexpli- 
cable, excepting on the principle laid down by Dr Wells. The 
facts, I believe, were shortly as follows : The heat of the exter- 
nal air was 27°, that inside the coach, the windows being shut, 
54°. The inner surface of the windows, incrusted with ice, had 
a temperature of 32°. The outer surface of the glass was dry, 
and the front windows, shaded by the cabriolet, were free of 
ice. On lowering the window about half an inch, the crust of 
ice disappeared very shortly, and the temperature of the air in- 
side the coach was considerably diminished. These facts, how- 
ever, admit of explanation on a principle different from that laid 
down by Dr Wells. Before the window was let down the air 
inside the coach, having a temperature of 54°, would necessarily 
acquire much moisture from the perspiration and breath of the 
inmates ; while the glass of the window was reduced to 32°, by 
the constant action of a current of air 5° colder, on its outer sur- 
face. The external air being 27° colder than the internal, and 
having, consequently, a much greater specific gravity, would, 
on letting down the window, rush in, and, displacing the warm 
moist air, would become heated in its turn, and thereby have 
its capacity for moisture greatly increased. It would thus be 
* Annals of Philosophy. 
