of Edinburgh, Session 1883-84. 
683 
pected change in the manner of working, this defect has not been of 
importance, and the instrument has been found to be very service- 
able. The bulb is very long, being 55 mm. or more than 2 inches, 
and has a diameter at the top of 3 mm. and of 2 mm. at the bottom. 
It is graduated from 0° to 100° Fabr., and has an expansion at the 
top of the tube to prevent bursting when heated over 100°. The 
large capacity of the bulb has given a long and easily read scale, 
there being almost 2 mm. between each degree. 
It may be remembered that this thermometer was constructed for 
the purpose of following up a line of investigation suggested by 
the experiments on the temperature of large and small bodies 
exposed to radiation. It bad been found that the smaller a body 
was, the nearer its temperature was to that of the air surrounding 
it, because it was more quickly deprived, by the passing air, of 
the beat received by radiation from surrounding objects ; and there 
seemed reason for supposing that if the bulb of a thermometer was 
smaii enough radiation would not beat it to a perceptible degree. 
This thermometer was therefore constructed with the intention of 
seeing how nearly a thermometer with a very small bulb would 
indicate the true temperature of the air. 
Owing to an unexpected change in the development of this 
investigation, but few trials were made with this instrument as 
received from the maker. A few tests were, however, made. In 
these experiments the thermometer was placed under a horizontal 
sunshade, which protected it from all sunshine, and from nearly 
the whole of the sky radiation. The day on which the experiments 
were made was bright and warm, with a slight air from the east. 
The radiation thermometer already referred to showed a temperature 
of 140° in the sun. Under these conditions, the new thermometer 
always read just about a degree higher than the fan thermometer, 
and was generally more than half a degree lower than another 
thermometer with ordinary sized bulb placed alongside of it. It 
is, therefore, evident that this instrument, though better than 
an ordinary one, cannot be relied on to give the true tempera- 
ture of the air when shaded in the manner described ; as it would 
read correctly only on dull days, and be a degree more or less too 
high according to the brightness of the day. If the bulb of this 
thermometer had been made smaller, as ordered, it is possible the 
