PHILOSOPHICAL TRANSACTIONS. 
XI. On the Amount of the Radiation of Heat , at night , from the Earth, and from 
various bodies placed on or near the surface of the Earth. By James Glaisher, 
Esq., of the Royal Observatory at Greenwich. Communicated by G. B. Airy, 
Esq., F.R.S., Astronomer Royal, 8$c. 
Received January 14, — Read February 4, 1847. 
In the Report of the Committee of Physics of this Society in the year 1840, the 
measure of the radiation of heat at night from the earth was specially mentioned as 
being of importance to meteorology ; and it may be added that it is of the utmost 
importance to the economy of nature. 
As soon as the duties of the Magnetical and Meteorological Observatory permitted, 
I employed some time in making myself acquainted with all that was known upon 
the subject of radiation. The results of my researches were only a few papers in the 
Transactions of this Society, and the Treatise on Dew by Dr. Wells ; and in general 
I found a great want of good observations ; I therefore determined to pursue the 
subject with some degree of steadiness. The instrument recommended to be used in 
the report above referred to, was a self-registering minimum thermometer, placed in 
the focus of a polished metallic reflector ; and, in consequence of this recommenda- 
tion, the instrument has been in very general use ; it was, however, mentioned as 
being an imperfect instrument. 
The instrument being thus confessedly imperfect, it became exceedingly desirable 
to ascertain the amount of its errors ; and, to this end, to have very many compari- 
sons made between it and those instruments or methods which might be found less 
imperfect, so as to have a ready and certain means of converting the results derived 
from observations by it to other results, if it were found desirable so to do. With 
this view the thermometer, whose bulb was placed in the focus of a reflector, has been 
read, almost without exception, in every series of experiments. 
My first object was the obtaining instruments of the best possible kind, and I con- 
MDCCCXLVII. 
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