66 Proceedings of Boy al Society of Edinburgh, [jan. 17, 
son screen was closed with either a louvred or solid bottom the 
error was greatly reduced. 
After these tests were made, the Scottish Meteorological Society 
took up the matter, and made a number of comparative trials with 
the apparatus. The first of these tests were made at Granton in 
the summer of 1885 by Mr H. N. Dickson. After the Granton 
work was concluded, Mr Dickson took some of the screens to the 
top of Ben Nevis, continued the investigation there, and produced a 
most careful and elaborate set of observations under the conditions 
existing at the top of the mountain. The Ben Nevis work has not 
yet been published, hut Mr Dickson communicated some of the 
results of his work at Granton to the Royal Society of Edinburgh.* 
In this communication he gives curves of the temperatures for two 
days. These temperatures were taken by the fan apparatus, the 
silvered bulb, and one Stevenson screen with bottom open and 
another with it closed. On examining these curves I was much 
astonished to find that they confirmed none of the conclusions 
arrived at from trials made here. At Granton the fan and silvered 
bulb did not give the best results ; the silvered bulb read 
highest throughout the whole of the second day, and further there 
was little to choose between, in the readings of the Stevenson 
sereens with open or closed bottoms. 
These results obtained by Mr Dickson at Granton are so different 
from mine, that I thought it necessary to reconsider the matter, 
and again go over my work, under the conditions existing here. In 
my first trials I had only one Stevenson screen ; its readings were 
compared with those given by the fan apparatus and the thermo- 
meter with silvered bulb ; and, comparing the readings with the 
standards when the bottom was out and when it was in, the 
result was greatly in favour of the observations made with the 
bottom closed. Mr Dickson made his trials with two screens, — one 
sent by me with louvred bottom and double top, and another of 
the ordinary pattern, that is, with bottom open. 
In the autumn, my old screen with its louvred bottom was 
returned from the trials at Granton and Ben Nevis, and I obtained 
a new one of the standard pattern and exactly similar, only with 
open bottom and single top ; the latter of these screens in the 
* Proc. Pioy. Soc. Pdin., No. 120, p. 199. 
