of Edinlmrrjh, Session 1883-84. 
673 
hung up in sunshine, to see the effect of size on objects exposed to 
the direct rays of the sun. The following table shows the result : — 
Clean Bulb. 
Blackened 
Bulb 
T' diameter. 
Box 
2 " diameter. 
Box 
2" diameter. 
Box 
4" diameter. 
78° 
8or 
84° 
89°-5 
95° 
Objection might be taken to the manner in which the above 
experiment was made. It might be asked, for instance, Was not 
part of the difference of temperature due to the heat received on the 
side of the box next the sun being quickly conducted to the shade 
side, in the small boxes, and carried away by the wind, while in the 
large boxes the heat could only be slowly conveyed to the shade 
side by the hot air in the box To check these results, I filled the 
large box with a liquid, using turpentine, on account of its small 
specific heat. Placing this box in sunshine, and alongside of it the 
half-inch box, in which was fixed a maximum registering thermo- 
meter, it was found that the large box attained a temperature of 96°, 
while the thermometer in small one indicated a maximum of 85°, 
thus confirming the result of the previous experiment. 
We might look on these boxes with attached thermometers 
simply as thermometers with very large bulbs. We see from 
this that the indications of correct thermometers may vary when 
hung in certain positions, owing to a difference in the size of 
their bulbs. No doubt these are very extreme sizes, still I find that 
the size of the bulbs of the thermometers in general use does affect 
their indications. Selecting two thermometers, one with a large and 
one with a small bulb, I hung them up beside each other under 
the shade, and found that the one with the smallest bulb indi- 
cated a temperature about half a degree lower than the large one. 
I may say that the precaution was taken of checking the readings of 
these thermometers in water at the same temperature as the air. It 
is possible that a difference in the thickness of the walls of ’the bulbs 
may have caused the large thermometer to absorb more heat than 
the other, but this can scarcely account for the whole difference. 
Not only will the size of the bulbs affect the indications in the 
open air, but the manner in which the thermometer is mounted will 
2 X 
VOL. XII. 
