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too high, causing the readings of any hygrometrical instru- 
ment to show too low a percentage of moisture. Some 
observations made for three years at the Belvedere seem to 
me of little value on account of being made in a Stevenson’s 
screen exposed to the sun ; but on this point I do not now 
wish to speak too positively, as I purpose shortly comparing 
all the observations made in Davos in order to find out what 
screen should be used. 
It must not be forgotten that those causes which give us 
so much solar radiation also bring about great terrestrial 
radiation. No exact observations have yet been made here 
on this subject of terrestrial radiation, and as I only had 
a place very much exposed to the ravages of dogs and 
children I could not place out a valuable instrument, but 
put out a cheap minimum thermometer about an inch above 
the snow, with the bulb painted white, because I considered 
that in this way the radiation from the snow was best 
tested. I had it out for about four weeks, when it was 
stolen. The results were that the mean minimum from the 
6th to 28th February inclusive was 5*5°Fahr., which is 
about thirteen and a half degrees lower than the mean of 
the minima of the shade temperature, but as the instruments 
were not absolutely reliable I cannot give the exact differ- 
ence. This means that on a fine day the difference between 
the minimum terrestrial and maximum solar radiation is at 
least 100° F.; on one occasion it was 122*8 degrees. At 
nine o’clock (viz., before the sun was shining in the valley 
generally) I registered — 8° Fahr. with the radiation ther- 
mometer, and at the same time the temperature of the air 
was 19*2° F. or a difference of 22*2 degrees. I had the 
opportunity of seeing that thermometers placed, unprotected, 
on the side of a house, as is so often done by those who 
take “ window observations,” gave morning results fairly 
parallel with these terrestrial observations, and did not give 
the temperature of the air at all, and it seems that both the 
