148 
MR. GLAISHER ON THE RADIATION OF HEAT, 
Table (Continued). 
Situation of the thermometer, its bulb, or the substance under which 
it was placed, being fully exposed to the sky. 
Whole 
number of 
compari- 
sons. 
Whole sum of the 
excesses of the 
readings of the 
thermometer in 
air at the height 
of 4 feet, above 
those placed as 
stated in the 
first column. 
Mean 
excess of 
the reading 
of the ther- 
mometer in 
air. 
Relative 
excess, that 
of long 
grass being 
represented 
by 1000, or 
compara- 
tive radia- 
ting power. 
Remark.. 
On orange lambs’ wool 
33 
233-3 
7-07 
844 
These observations were 
On yellow lambs’ wool 
33 
239-5 
7-26 
855 
I always simultaneous. 
On red lambs’ wool 
33 
223-3 
6-77 
807 
On crimson lambs’ wool 
33 
225-3 
6-83 
814 
J 
On garden mould 
151 
598-5 
3-96 
472 
] These observations were ge- 
On gravel 
149 
361-4 
2-42 
288 
j " nerally simultaneous. 
On river sand 
157 
599-0 
3-81 
454 
1 See simultaneous observa- 
On river sand on the raised board 
25 
127-6 
510 
J tions. 
On tinfoil 
33 
129-8 
3-94 
470 
On lead 
224 
1421-7 
6-35 
757 
1 See simultaneous observa- 
On lead six inches high 
13 
53-2 
410 
j tions. 
On lead one foot high 
48 
261-3 
5-44 
On lead three feet high 
2 
10-5 
5-25 
On copper 
172 
1210-5 
7-04 
839 
On iron 
161 
868-2 
5-39 
642 
1 See simultaneous observa- 
On zinc 
213 
1217-9 
5-71 
681 
j tions. 
On zinc six inches high 
29 
175-2 
604 
On zinc one foot high 
6 
29-4 
4 90 
On zinc three feet high 
6 
270 
4-50 
On zinc four feet high 
4 
13-2 
3-30 
On white tin 
112 
616-6 
5-51 
657 
On white tin one inch high 
75 
378-0 
5 04 
601 
] Generally simultaneous ob- 
On blackened tin 
104 
672-2 
6-46 
770 
J servations. 
In focus of metallic parabolic reflector 
464 
3340-7 
720 
858 
On the raised board 
50 
323-4 
6-49 
773 
On saw-dust in a box on the raised hoard 
37 
189-3 
5-12 
610 
Nine inches above wood and protected from lateral wind 
394 
1236-8 
3 11 
371 
On brick 
46 
143-5 
312 
372 
On pantile 
111 
437-2 
3-94 
470 
On slate 
100 
481-1 
4-81 
573 
On glass 
163 
1182-3 
7-25 
864 
f These observations were ge- 
On glass one inch high 
156 
954 1 
6 11 
728 
J nerally simultaneous, and with 
One quarter of an inch above water 
83 
225-7 
2-72 
324 
L under the glass. 
On paper on the raised hoard 
8 
41-2 
5-15 
614 
On hare-skin 
70 
773 1 
11-04 
1316 
On rabbit-skin 
59 
6132 
10-40 
1240 
1 See simultaneous observa- 
On stone 
154 
503-3 
3-27 
390 
J tions. 
Number of observations of the thermometer in air, and 1 
its mean reading / 
487 
43-7 
No certain difference was found from many simultaneous experiments on lead less than the twentieth of an inch in thickness, and 
lead a quarter of an inch in thickness ; the observations are everywhere used as lead, independently of its thickness. The same remark 
applies to the three different thicknesses of zinc, and to the three different stones used ; and their results have been combined as one 
result for “ zinc,” and as one result for “ stones” in the final result. 
Some of the particulars which we may learn from the preceding table are the fol- 
lowing. 
The first results contained in it are those relating to grass, whose radiating power 
appears to be such, that the reading of a thermometer when placed on it when long, 
is less than when it is placed on short by 1 0, 1 ; the next result relating to grass is 
that of the temperature on the surface of the soil under it, which is such that the 
reading of a thermometer under long, exceeds that under short by 1 °* 1 ; being ex- 
actly the same amount in excess under as it was in defect on the top ; and hence 
the cause of the difference of the readings on the top of long and short grass arises 
solely from the greater quantity of heat conducted to the surface of the latter from 
