METEOROLOGY OF 1 897. 
7 
thin muslin and water is applied before the observation. 
The stationary form of psychrometer is especially unsat- 
isfactory in freezing weather because it is difficult to obtain 
sufficiently rapid evaporation from the film of ice. 
THERMOGRAPH. 
a pen to 
§11. Figure 3 
represents the type 
of therm o g r a p h 
which has been 
used since 1890. 
This has been 
found to be a very 
satisfactory instru- 
ment in most re- 
spects. It is a 
pattern made in 
Paris by the firm 
of Richard Bros., 
from whom we 
have obtained a 
number of our self- 
recording instru- 
ments. d'he ther- 
mometer consists 
of a metallic tube, 
shown at the right 
of the instrument, 
which is filled with 
alcohol or ether. 
One end of the 
tube is fastened, 
the other free. As 
the temperature 
changes, the expan- 
sion of the liquid 
changes the curva- 
ture of this tube, 
and the movement 
of the free end act- 
ing through a ser- 
ies of levers, causes 
rise or fall according as the temperature increases 
