a : ANNIVERSARY ADDRESS. 29 
so much to do with rain? Experience teaches us that the great 
bulk of rain falls without any electrical manifestation—even 
heavy tropical rains ; and it is no uncommon thing for clouds to 
give rise to tremendous electrical discharges and not a drop of 
rain, It is evident, therefore, that the two have no necessary 
_ connection. 
I have not yet referred to the vibrations of sound as a cause of 
rain. The laws under which water is held in the atmosphere are 
' well understood, and, to any one who knows these conditions, the 
idea that vibration will cause its precipitation is absurd. Sound- 
waves do not alter the temperature or tension of the air except in 
a very slight and temporary way, and without change in one or 
both water cannot be deposited. If it is said that the firing of 
cannon has caused rain, the reply is that the statement rests upon 
the incomplete testimony of a few persons who did not inquire 
into the facts as carefully as they ought to have done ; and, on 
the other hand, there is the testimony of two generations in France, 
who by constant experiment ‘were convinced that the sound of 
guns had the opposite effect ;and severe as M. Arago was upon them 
for their belief i in fine weather made by cannon, they had quite as 
much evidence in favour of their view as those have who hold the 
_ ‘Modern one. It is estimated that in the battle of Sedan about 
300 tons of gunpowder were used during the three days that the 
fight lasted ; and the enormous amount of heated gases thus set free, 
: - and the heat of, say 300,000 men, together with the actual 
: ‘Moisture set free might, if circumstances were favourable, disturb 
‘the equilibrium and cause rain; but none fell during the three days. 
On the fourth day, that is, the first after the battle, it did rain ; but, 
te economical production of rain under ordinary circumstances ; 
om our only hanes would be to take advantage of a time when 
mo a upwards, and once 
