154 
MR. GLAISHER ON THE RADIATION OF HEAT, 
at which other large differences took place, with their amounts, will be seen in 
Section II. 
The next class of bodies consisted of black and white wadding, flannel, and wool of 
different kinds and colours. Of these, black and white wadding exhibited the lowest 
readings, and were nearly equal in amount ; flannel was the next in order, and the 
various-coloured lambs’ wool were the next ; but the differences between those bodies 
with respect to their radiating powers were not large ; they were all, however, in- 
ferior in their radiating powers to bodies of the first class. It will be seen in 
Table XLV. that the numbers opposite to flannel, yellow and blue cotton wool, when 
those substances were placed on the raised board, are larger than those numbers with 
the same substances placed upon grass ; these differences most probably arose from 
the different quantities of heat which they received from the parts beneath, the several 
substances being slow conductors of heat. 
The observations upon the coloured wools were too few to indicate positively the 
influence of colour, nevertheless they were all good and simultaneous experiments. 
The order of their radiating power is black the lowest, then green, white, crimson, 
scarlet, orange, yellow, dark blue and light blue successively, the difference between 
light blue and black being 1°‘3. The same parcels of wool were exposed to the direct 
rays of the sun many times, and as nearly similarly situated as possible. The mean 
of fifty-eight simultaneous readings of the thermometers placed on them gave — 
Black 105 
Yellow 105 
Scarlet 107 
Orange 109 
White 110 
Green 110 
Crimson 110 
Dark blue 110 
Light blue 121 
Thus black and light blue are at the extremes of the absorptive powers, and so 
far confirm the results obtained by the night observations, as the absorptive power 
of substances is proportional to their radiating power. 
But as these results with respect to colours may have been affected with the par- 
ticular parcels of wool I used, and different results might have been obtained had 
other parcels been used, I do not place much confidence in them ; yet, so far as I 
could discover, each parcel was equal in thickness, hardness, and in fact in every 
respect except that of colour. 
Bodies in the state of powder, placed on the raised board, formed a third class of 
substances. These were black-lead, charcoal, whiting, chalk, lamp-black and river- 
