————————e ee — 
PRESENT STATE OF OUR KNOWLEDGE OF THE UPPER ATMOSPHERE. 73 
increase of height. Gay-Lussac found the rate of fall of temperature 
to be 1° F. per 300 feet and that the magnetic force increased with height. 
No further investigation was made until 1850, when Messrs. Barral and 
Bixio made two remarkable ascents from Paris. They demonstrated the 
great thickness (about 15,000 feet) of some cloud masses and noted that 
while the light from the sky was polarised, that reflected from the clouds 
was not. At 23,000 feet they encountered a cloud consisting of ice 
particles.' The British Association first took part in the work in 1852, 
when Mr. John Welsh made four ascents from the Kew Observatory. The 
object of the ascents was to find the rate of diminution of temperature and 
change of humidity, to collect samples of air, and to examine the light from 
the clouds for polarisation.? Recognising the probable effect of the sun 
on exposed thermometers, Welsh enclosed his thermometers in a polished 
metal tube through which air was forced by bellows, thus instituting the 
aspirated apparatus perfected later by Dr. R. Assmann of Berlin. The 
thermometers were very sensitive, falling through 20° F. in 11 seconds 
on being taken from a warm toa cold room. He attained heights ranging 
from 4 to 7 km., and found that the temperature fell uniformly, until at 
a certain height, which varied on different days, the fall was arrested and 
the temperature remained practically constant through 600 to 900 metres. 
The uniform diminution was then resumed, but at a less rapid rate. The 
seasonal variation of the rate of fall of temperature was demonstrated. 
It was found that the light reflected from clouds was unpolarised.* 
The experiments in connection with the British Association were 
continued by a Committee appointed at the Manchester meeting in 1861. 
The experimental work was undertaken by Mr. Glaisher, who with Mr. 
Coxwell?made twenty-eight ascents during the period July 17, 1862, to 
May 1866.4 The chief objects of the investigation were to find the laws 
of variation of temperature and humidity with height, and to examine 
the variation of magnetic force and electric potential. 
Glaisher at first employed Welsh’s aspirated thermometers, but 
noticing that these recorded the same values as the exposed instruments 
he discontinued the aspiration. Subsequent observations have shown that 
the agreement between the indications of aspirated and unaspirated 
instruments was due to faulty exposure in the balloon-car. He took 
also maximum and minimum thermometers, ozone papers, and an electro- 
meter lent by Professor W. Thomson of Glasgow (Lord Kelvin). 
As the number of observations increased the conclusions drawn 
became more uncertain. To quote Glaisher’s words :— 
It was found that those taken in the morning hours did not accord 
with those taken in the afternoon hours, nor did those taken at one time 
of the year agree with those taken at other times of the year.’ ” 
In cloudy weather the rate of fall was 1° F. per 300 feet, but in clear 
weather 1° F. per 160 feet at first, and only 1° F. per 1,000 feet at 6 miles. 
Observations at night were made with the help of miners’ lamps, when it 
was found that the temperature rose as the height increased. The results 
for humidity were similar to those of Welsh. At a height of five miles 
(8 km.) there was almost complete absence of water vapour. The time of 
vibration of a suspended magnet was found to diminish with increase 
! Nature, xviii. p. 639. 2 Brit. Assoc. Reports, 1852, p. xxix. 
§ Phil. Trans., 1853. 4 Brit. Assoc. Reports, 1861-66. 
5 Brit. Assoc. Reports, 1862, pp. 31, 376 ; 1863, p. 426; 1864, p. 195; 1865, p. 145 ; 
1866, p. 367. 
