88 REPORTS ON THE STATE OF SCIENCE. 
He standardises the instruments (1) at normal pressure in moist and 
dry atmosphere ; (2) at reduced pressure and temperature in moist and 
dry atmosphere. 
In testing the Dines instrument the whole instrument is placed in 
an alcohol bath under the glass receiver of an air-pump. In this way 
the temperature correction of the barometer is found, at the same time 
as the thermometer is tested, by cooling the bath to various tempera- 
tures with carbonic-acid snow and exhausting the receiver in steps down 
to about 50 mm. at each temperature. 
Allowance is made for the pressure due to the depth of submersion 
of the aneroid in the alcohol. The alcohol is kept in circulation by the 
vigorous boiling off of the carbonic acid. (This is sufficient at times to 
make the liquid boil over the sides of the reservoir.) 
The temperature correction is more complicated than that of other 
instruments owing to the aneroid being only partially exhausted. It 
cannot be represented by a simple mathematical formula. A separate 
calibration curve is therefore drawn for each temperature, and the 
corrected pressures are read off from the curves. 
The temperature scales of all the different types of instruments are 
found to be linear, and the temperatures are calculated by means of a 
coefficient. 
The hygrometer scale is not quite uniform, and a correction is applied 
to the humidity indicated. 
Accuracy of Results.—The possible errors which may arise in observa- 
tions by means of kites have been practically eliminated by the con- 
struction of instruments almost completely unaffected by the shocks 
which occur during an ordinary ascent. 
No appreciable error can arise from solar radiation, because the 
wind which is necessary to raise the kite provides sufficient ventila- 
tion. The lag of the Marvin instrument is 1° F. when the temperature 
changes at the rate of 1°°5 F. per minute, corresponding to the ordinary 
rise or fall of the kite at the rate of 500 feet perminute.' The lag of other 
instruments is less. 
The effects of solar radiation in manned and captive balloon observa- 
tions on the Continent have been minimised by the use of aspirated 
instruments, while in England such ascents are made either near sunset 
or before sunrise, except when the sky is completely overcast. 
The chief errors in the observations arise in the ballons-sondes results. 
At the extreme heights reached by free balloons solar radiation is 
very intense, and may raise the temperature of an unventilated thermo- 
meter as much as 50° C. above that of the air.” 
This effect has been largely eliminated by the use of rubber balloons 
and instruments enclosed in highly polished ventilation tubes, and in 
many of the Assmann instruments by the additional precaution of as- 
piration by means of an electrically driven fan giving a current of 4 to 
5 m.p.s. The lag of the instrument has been diminished by the use of 
Bourdon tube barometers, the bimetallic thermometers of Teisserenc 
i and Dines, the tube thermometer of Hergesell, and ventilation 
tubes. 
The ventilation produced by the ascent of the balloon is now generally 
1 Frank. Instit. Journ., 148, pp. 241-259, October 1899. 
? Assmann, Preuss. Akad. Wiss. Berlin, Sits. Ber, 24, pp. 495-504, and Inter- 
national Ascents Pavlovsk, November 8, 1906. 
