171 
the gold cup is sometimes reduced 20 — 30 degrees* before 
dew point is obtained, it is evidently necessary that it 
should be protected from the wind ; but even then we may 
be sure that the outside of the cup will be slightly warmer 
than the inside. When this form of hygrometer has been 
more used, I think that we shall better understand the 
Davos climate. 
Position of Instruments. 
In order to obtain the relative moisture correctly, it is 
of course of the utmost importance that the instruments 
should be correctly placed and protected; and I have there- 
fore given some attention to this question, which seems to 
be one of the most difficult meteorological problems, and 
is now receiving much attention from meteorologists. It 
will be seen that I have on both occasions placed my screen 
in the shade, and I think that I may now definitely say 
that such an arrangement is necessary, for here when the 
solar radiation is so intense and the movement of the air 
but slight, a Stevenson’s screen, as now commonly used in 
England, is warmed by the sun,-f* so that the temperature is 
# On April 7th, seeing the hair hygrometer showed the air to he very 
dry (under 17 per cent), I used the Regnault and found the dew point 
4° F. with the air temperature 49-5° F., thus giving about 14£ per cent 
of moisture. On this occasion, therefore, the temperature of the cup 
was reduced 85 degrees. 
f In the pamphlet to which I have already alluded, and which was 
hut a youthful production, I gave my measurements of the solar radia- 
tion as taken with a hlack hulh thermometer in vacuo, and I think it 
well to repeat them here, because some similar observations made since 
by the Rev. Mr. Redford, F.M.S., and others, for four years at the hotel 
Belvedere, have found their way into a very large number of medical 
publications, although they are entirely incorrect in consequence of the 
radiation thermometer being placed upon the white screen, thus regis- 
tering, instead of 100° F., about 120° F., and instead of 120° F, about 
140—150° F. r — 1870 , r— 1871 — , 
Nov. Dec. Jan. Feb. 
Mean of daily Maxima 95’IF. ... 73-9 F. ... 77'3 ... 104-3 
Maxima of month 115-4F. ... 1151F. ... 117-2 ... 126-0 
Mean of the Maxima of Air 
Temperature, in shade 85-8 F. ... 41-9 F. 43-8 F. 32*4 
