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exposed Stevenson’s screen or a metal box attached to the 
side of a house, as used by the Swiss, must be very much 
influenced by terrestrial radiation.* 
Mr. Demmer, the intelligent proprietor of the Angieterre 
Hotel, shortly before my arrival put up a Stevenson’s 
screen in a provisional position, and as soon as he has com- 
pleted some building and is satisfied as to the best means of 
protecting the instruments, intends to make some observa- 
tions. He very kindly allowed me to make some compari- 
sons with the result obtained in my box, and as his instru- 
ments were made by Casella and tested in Kew, and those 
I was using also by Casella, they may be relied upon. 
From ten observations made for the purpose, I find that 
the average range in temperature from 9 a.m. to 1 p.m. is 
5 degrees more than I obtained in my shaded box, and 
upon one occasion the range was 9 ’2° F. more than mine. 
Formula. 
But even when we have got the observations correctly 
taken we are by no means at the end of our difficulties, as 
the different formulae used to calculate the moisture from 
the dry and wet bulbs give materially different results. In 
England, Glaisher’s tables, or Apjohn’s formula are mostly 
used ; whereas in Germany and Switzerland tables based on 
Kegnault’s formula or the formula itself are used. 
In Glaisher’s tables we find under dry 36°, wet 30° F., 
relative moisture, 53 per cent at sea level, whereas Jelinekf 
for the same temperatures gives 47 per cent. With a very 
cold and dry air, the difference would be much larger, and 
the differences of the various formulse are in some cases 
increased when we give the correction for diminished baro- 
# Prof. H. Wild describes a large wooden screen under wbicli the 
metal boxes as used in Switzerland can be hung, and probably this would 
be the most satisfactory plan for Davos. Aufstellung der Thermometer 
z. Bestimm. d. wahren Lufttemp. Ak. St. Petersburg, 1878. 
f Psychrom. Tafeln. fur das hundertth. Thermom. von Dr. Jelinek. 
Wien, 1876. 
