146 
MR. GLAISHER ON THE RADIATION OF HEAT, 
conducting heat was bad, such as raw wool, flax, hare-skin and rabbit-skin, and con- 
trary to expectation, even on metals, whose power for conducting heat is good. 
In Table XLIV. the reading of a thermometer on raw wool was 25° less, whilst 
another placed at 8 feet from the ground and fully exposed to the sky, was 3 0, 5 
greater than that in air at the height of 4 feet and protected from radiation, and thus 
a difference of 28 0, 5 existed between the readings of two thermometers, the one 
placed on raw wool, and the other in air at the height of 8 feet. This difference was 
the greatest that I have ever seen, and it occurred in 1844, on April 8 d , at 8 h . 
The general agreement in the relative radiating powers of the different substances 
on different nights, and many other particulars, will be best seen by consulting 
Tables I. to XLIV. 
I shall now proceed to explain the formation of the following table of the mean 
results derived from all the observations. 
The mean of the numbers was taken in every group of results contained in Tables 
I. to XLV., for every different substance or different position of the thermometer in 
each period of observation, thus forming three large tables ; from these a fourth 
table was formed by combining the mean results for every substance, according to 
the number of observations from which each had been deduced, omitting, however, 
all those which had been taken when the excess of air-temperature above that of long 
grass temperature was less than 2 0# . From the numbers in this last table the next 
table was formed. 
i 
The last column but two in the following table contains the mean excess of the 
reading of the thermometer in air above those placed as stated in the first column, 
derived from all the observations made on each substance, &c. These numbers are 
smaller than they would have been had the observations been made in a wide and 
open plain (see introductory remarks), and also if the thermometer in the air had been 
perfectly protected from the effects of radiation (see remarks following Table XLV.). 
The numbers in the last column but one represent the relative radiating power of the 
several substances, that of long grass being considered as 1000. It is probable that 
these numbers are very accurate, for had the results in the preceding columns been 
larger than they are, they would have been relatively so, consequently the numbers 
in this column would not have been affected. 
In most cases the experiments have been sufficiently numerous to give results 
worthy of entire confidence, the numbers in this column having been deduced from 
upwards of 10,000 experiments. 
* These four Tables are in MSS. and placed with the series of observations. 
