1921.] The Highth Indian Science Congress. exil 
easy matter, for the silver on the plates has to be deposited in 
so light a film that there shall occur no such adhesion as could 
lead to stripping by the pens, and consequently the records are 
photographically thin and their enlargements weak. 
34. The first! shows conditions in the cold weather, Jan. 
25, 1917, when weather was dry and fine in Agra, but unsettled 
in the hills to the north. In this record it is clear that although 
the humidity at the ground was low, saturation was reached 
at the level where clouds might develop and result in wet 
weather. Asa matter of fact rain fell two days later. 
The second shows similar ground surface conditions at the 
same time of year, but with this difference above, that there 
is no indication of increasing humidity to bring its chance 
Fig. 23. 
ofrain. Weather remained dry during the ten days around this 
flight. 
Feb. 16, 1917.—The next record is in mid-February, when 
weather had been dry everywhere for six days, and continued £0 
afterwards for some time. The humidity trace shows at all 
heights an absence of the water vapour which is essential to 
March 1, 1917.—Passing to March, we have in this record 
great dryness at the ground, but higher up there is ample 
material for rainfall. The weather had been dry for a week 
over north-west India, but proved wet on the following day. 
March 13, 1917.—Compare with this the next record for a 
| ‘There were eight diagrams: only one is reproduced here. 
