METEOROI.OGV OF 1 897. 
9 
rents of air pass, with very little change in the dew point. 
At other times the wet bulb thermometer will suddenly rise 
or fall, showing a marked change in the moisture conditions 
of the air without a corresponding change in temperature. 
THE BAROMETER. 
§13. The barometer which has been used was made by 
Green, and consists of a mercurial barometer with adjust- 
able cistern. I'he height of the mercurial column is meas- 
ured from the mercury in the cistern to the top of the 
mercurial column near the upper part of the tube. The 
mercury in the cistern is always brought to the same 
height by a screw in the bottom. The attached thermom- 
eter shows the temperature of the mercurial column. This 
is read at each observation, and as the mercury expands or 
contracts with change of temperature a correction is made 
to the readings of the instrument to allow for the expansion 
of the mercury, and also for the change in length of the 
brass scale at the side of the instrument. The heights 
given in the tables are the heights corrected for tempera- 
ture, or are the pressures of the barometer for a uniform 
teperature of 32", but measured by a scale of correct length 
at a temperature of 62'’. The station has two barometers 
of this type, one of which was in use at the sub-station in 
the San Luis Valley for some years, until, with a change in 
location of the stati(jn, the barometer was injured. 
BAROGRAPH. 
Fiff. 
