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56 TRANSACTIONS OF THE 
struments fall to the earth. In order to protect the instru- 
ment in its falls so that the record and instrument will not 
be greatly injured, two devices are used. Either the larger 
balloon contains a smaller balloon which is large enough 
greatly to lessen the fall, or a parachute is used which 
opens as soon as the instrument commences to fall. In 
addition a basket work is arranged around the instrument 
to ease up the shock. These plans have all been success- 
fully carried out, the instruments receiving little or no 
injury. The instrument, of course, is carried up into re- 
gions of very low temperatures and the record is secured 
in two ways: first, an ink is used which does not evaporate 
or freeze, and is made of glycerine with an aniline dye. A 
second way is by using a sheet similar to those used on a 
seismograph. The sheet as you know has a deposit of soot 
on it and instead of an inked pen a stylus is employed. 
The rate of increase or decrease in temperature as 
higher altitudes are reached is called the temperature 
gradient. Air is cooler as higher altitudes are attained, 
and it is the custom to say that the decrease is at the rate 
of 1 degree for every 183 feet, but this is the adiabatic 
rate. By adiabatic heating and cooling we mean the in- 
crease or decrease in heat due to change in pressure, that 
is without gain from or loss to outside space. When a 
quantity of air rises it expands and does work which con- 
sumes a certain amount of heat energy; and conversely 
when it descends work is done upon it and it regains 
the heat that was lost. 
This rate varies greatly according to the constituents 
of the atmosphere. Water vapor causes a considerable 
change from the dry adiabatic. 
The changes due to day and night and to the various 
seasons are felt in the upper as well as in the lower atmos- 
phere, but not to such a great extent. In the free air about 
3 or 4 thousand feet high no changes are felt due to the 
rotation of the earth on its axis. 
The seasonal change, however, is more pronounced, 
and is about half as great in the upper as in the lower atmos- 
phere. 
