142 THE EEASON WHY. 



" The clouds poured out water ; the skies sent out a sound ; thine arrows also 

 went abroad. 



5 beats, 1% miles. 



6 beats, 1 miles. 



7 beats, If miles. 



8 beats, 2 miles, &c. 



Attention should be paid to the direction and speed of the wind, 

 and some modifications of the calculation be made accordingly. 

 Persons between 20 and 40 years of age should count Jive beats of 

 the pulse to a mile ; under 20, six beats. 



624. Why are electric storms more frequent in hot than 

 in cold weather ? 



Because of the greater evaporation, as the effect of heat ; and 

 also of the effect of heat upon the particles of all bodies. 



625. Why do electric storms frequently occur after a 

 duration of dry weather ? 



Because dry air, being a bad conductor, prevents the opposite 

 electricities from finding their equilibrium. 



626. Why is a flash of lightning generally succeeded by 

 heavy rain ? 



Because the electrical discharge destroys the vescicles of the 

 vapours. If a number of small soap-bubbles floating in the air 

 were suddenly broken by a violent commotion of the atmosphere, 

 the thin films of the bubbles would form dmps of water, and fall 

 like rain. 



627. Why is an electrical discharge usually followed by a 

 gust of wind? 



Because the equilibrium of the atmosphere is disturbed by the 

 heat and velocity of lightning, and the condensation of vapour. 

 Air, therefore, rushes towards those parts where a degree of vacuity 

 or rarefaction has been produced. 



628. What is a thunderbolt ? 



The name thunderbolt is applied to an electrical discharge, when 

 the lightning appears to be developed with the greatest intensity 

 around a nucleus, or centre, as though it contained a burning body. 

 But there is, in reality, no such thing as a thunderbolt. 



