MR. GLAISHER ON THE RADIATION OF HEAT. 
161 
Table XLVUI. Abstract of Special Simultaneous Observations. 
Situation of the thermometer. 
Excesss of 
air-tempe- 
rature 
above the 
reading of 
thermo- 
meter. 
Number of 
simulta- 
neous ob- 
servations. 
Remarks. 
One inch above grass 
o 
9-0 
9 
The observations at the height of two inches were made on 
one night only. 
Two inches above grass 
5-0 
On white unwrought cotton wool ■ 
f on grass 
9-4 
1G 
It would seem that the amount of radiation from the raised 
on the raised board 
8-8 
board was less than that from the same substance on the ground. 
n f on Grass 
9-0 
11 
The amount of radiation from flax on the raised board decidedly 
On flax < ~ ■ a u a 
l on the raised board 
6-9 
the smaller. 
5-6 
25 
The sand on the board was a small quantity, w'hilst that on the 
0n sand {on the raised board 
51 
ground was a large quantity ; the amount of radiation from sand 
on the raised board was the smaller. 
f thin 
51 
31 
From these it would appear that the thickness of a metal has 
no influence on the amount of its radiating power. 
On zinc < moderately thick 
5-0 
[thick 
51 
On firestone 
3-3 
31 
The circumstance of Purbeck stone having a result larger than 
On Pnrbeck stone 
37 
the other two is probably accidental, as on many nights its results 
On Portland stone 
3-3 
were less than those of the other stones. 
On lead on grass 
6*5 
12 
The increase in the readings of a thermometer placed on a 
metal, raised in the air, is decided. 
On lead six inches above grass placed horizontally 
4-5 
In air at eight feet high 
0-8 
10 
The results are identical, and therefore in Table XLV. such 
In air at ten feet high 
0-8 
should be the case in the mean. i 
The observations at ten feet were made on one night only. 
In air at twelve feet high 
0-8 
On lead one foot high 
5-5 
2 
The increase in the readings of a thermometer with height is 
On lead three feet high 
5-3 
indicated. 
The remarks in the last column indicate the results of the experiments ; those rela- 
ting to the different readings of a thermometer when placed on the same substance on 
the raised board and on the grass, seem to exhibit in a decided manner that more 
heat had passed from the board to the surface of the substance than had passed from 
the grass to it, causing the reading of the thermometers to be increased ; the amount 
of this increase appears to be about half a degree, and this amount should be applied 
subtractively to all readings on substances placed on the raised board, or additively 
to all differences between their readings and those in air at the height of four feet. 
In Table XLV. the results from all substances in powder were deduced from 
observations on the raised board, and from this investigation all these results should 
be increased by half a degree : in the same table the results from blue and yellow 
jeweller’s wool and from raw silk exhibit a greater degree of cold on the raised board 
than when they were on grass ; but these substances were never observed simulta- 
neously in both positions, and they were only placed on the raised board on the finest 
and calmest nights, and in this latter position they require the same correction to be 
applied to them as it is necessary to apply to the other substances, whose results are 
deduced from observations taken on the raised board alone. 
MDCCCXLVII. 
Y 
