50 Journal of the Asiatic Society of Bengal. (February, 1908. 
lf further evidence be necessary as to the existence of cloud 
below the calm region, | may state that a balloon, while under ob- 
servation, has been frequently seen to enter a cloud at an elevation 
of less than 3,000 feet. 
height of about 2°, is generally about 8°, if there be no thunder. 
If at 18 miles’ distance the top of the cloud subtends an angle of 8°, 
then the heizht is roughly 12,000 feet. At that height stratus 
clouds form, and it is by no means uncommon to see the cumulus 
with its tip just visible over the layer of stratus through which it 
has penetrated. At the same time the layer of air in which the 
stratus cloud forms, appears to have a retarding effect on the as- 
cending cumulus, because, generally, the ascending motion ceases 
at that point. The top of the cloud becomes flat and is seen to 
drift away eastward. 
the aseensional motion should be sufficiently strong to over- 
come the obstacle which it meets at that level, then electrical effects 
begin. Itappears that in air which has not been seriously disturbed 
lightning begins at a height of about 15,000 feet. A thunder- 
storm occurs with a cumulus cloud which has risen above 12,000 
feet, and it may be to a height of between 20,000 and 30,000. The 
cirrous cloud which I have referred to above is formed in the highest 
layer to which the cumulus ascends. I have been unable to fix by 
this means the height of the cloud layer which is just above the 
calm region, that is, at a height of more than 4,000 feet. 
These measurements can be made with what is, I believe, fair 
accuracy with a line of cumuli at the distance I have mentioned or 
at a somewhat greater distance. But as they all depend upon the 
height of the base line, it will be evident that any considerable in- 
crease in the distance will materially lower that line towards the 
horizon and will, therefore, make its estimation more difficult owing 
aze, etc., as well as to the loss of measurable quantity, - 
I may mention, as showing the distance at which these cnmuli 
are visible in the clear air such as we have at the end of the mon- 
soon season, that I have seen just above the horizon the bright tip 
of a cloud which I knew from its appearance to be about 6,000 feet 
high. It must have been 200 to 300 miles away. 

12 ARENA SES 

