THE BEDSHIEL KATMS 299 



time to time, as continents and oceans change their relative 

 positions, the astronomical climates of certain other parts 

 are affected for the worse. It is part of the normal state 

 of things ; and there does not appear to be any necessity 

 for explaining these oft-recurring episodes by attributing 

 them to causes of an astronomical nature. 



Glaciers originate from snow ; the snow was formerly 

 aqueous vapour ; the aqueous vapour was at one time water ; 

 and formerly the water was distilled by the action of the 

 Sun. Therefore, without the Sun, there could be no glaciers, 

 and a Glacial Period in one part of the world is correlative 

 to tropical oceanic conditions in another. There must be a 

 boiler in one part and an active condenser in another, and 

 there must be means of communication between the two. 

 In the case we are considering the furnace of our boiler is 

 represented by the fierce rays of the tropical Sun, which 

 beats upon the surface of the Atlantic with almost incon- 

 ceivable intensity. The total daily sunheat at the Equator, 

 at the time of the Equinox, on each square foot of the 

 surface, is sufficient to lift 1,780,477 pounds weight one foot 

 high. That is to say, the quantity of heat received there 

 from the Sun is sufficient to get up steam enough to work 

 an engine that could do as much as that. That, of course, 

 is only another way of stating the fact that an enormous 

 quantity of water is evaporated by the Sun within the 

 tropics. Sea-water is turned into aqueous vapour by the 

 heat of the Sun, which heat, however, does not actually 

 warm the water very much, but disappears for a time in 

 the aqueous vapour ; which becomes what one may perhaps 

 be permitted to term a ''compound" of water and heat. 

 When that aqueous vapour is turned back again into water, 

 the hidden or latent heat is given out to the air, and as 

 much is set free as was used up in the first instance in 

 evaporating that same quantity of water. 



It may be as well to present the fact in other terms, 

 and, we may say, give Tyndall's statement that, in order 

 to heat one pound weight of sea-water one degree 

 Fahrenheit, almost ten times as much heat is required 

 as would suffice to raise the temperature of one pound 



