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sible care by frequently seeing that the bulb was in order, 
and no doubt Dr. Spengler was equally conscientious in his 
observations, yet it does seem that we both obtained too 
high a percentage of moisture 
The danger of error from these sources may to a large 
extent be overcome by having three thermometers, one of 
which will remain the dry bulb, whereas the other two 
should be kept wet, and one should have a recently formed 
sheet of ice, whereas the other should have an older one to 
which water has been added at least an hour before, for 
though in a few cases the temperature of evaporation was 
soon reached, yet as a rule this is not attained in an hour. 
I intend to use such a thermometer next winter, and con- 
sider that to obtain correct results this is almost a necessity, 
when the temperature is below freezing. As there is little 
wind here it would also be well to create a current by a 
revolving fan, as is done by the Italian meteorologists. 
The observations taken by Mr. Steffen since 1876 give for 
the winter months a materially less percentage of moisture in 
the air than Dr. Spengler obtained, and no doubt from the 
causes just mentioned. Unfortunately the position of Mr. 
Steffen’s house is very unfavourable for meteorological 
observations, as the instruments are sheltered by the house 
from the east and north winds, and a north-east wind 
very frequently blows, as valley wind, where his house is 
situated. 
Hair Hygrometer. 
Knowing the difficulty with the wet and dry bulb hygro- 
meter, it becomes an important question to find out how far 
hair hygrometers are available in cold weather, especially 
as the Swiss meteorologists are now using them, and there- 
fore I observed their action carefully to see if they would 
be useful for my next winter’s work, and I soon saw from 
the daily curve which they gave, compared with Mason’s, 
that they were not sufficiently sensitive, and did not alter 
