O72.| The Origin of the Great Cyclones. 423 
generate acyclone. The spark from a rushing locomotive 
may fire a prairie or a vast sea of forest, as has recently been 
instanced in the majestic and expansive conflagrations of 
the North-West; and, we must remember, that a sound 
generalisation does not demand of the physicist that he 
should assign a cause commensurate with every effect he 
sees ; but only such a cause as is equal to the origination 
of such an effect, or one that is sufficient to initiate it. 
The engineer of the Great Eastern moves with perfect ease 
the small lever which opens his steam valve, and, instantly, 
the mammoth steam-ship responds; her wheels begin at 
first slowly to revolve, condensation in her engines com- 
mences, and soon the vessel is pushing back the mighty 
waters and cleaving her way through the ocean. The touch 
of the engineer’s hand has only opened a way for the pent- 
up energy of her boilers to come into play; all the manual 
force exerted in occasioning this result, if directly applied 
to propelling the ship, would not have moved her an inch. 
To revert to the former illustration, it has not done as 
much to overcome the inertia of the floating leviathan 
as is exerted by the tender foot-fall of the chamois on the 
glacier of Mont Blanc, which sends the ice mass, whirling 
and leaping with terrific ruin, thousands of feet below. It 
must now be evident to the reader that there is a remarkable 
coincidence between the occurrence of West Indian hurri- 
canes and the conflict of the two great trade-winds. 
(rz). This coincidence is true in regard to PLACE. The 
West Indian cyclones are generated just where the 
hypothesis I have advanced would lead us to look for them. 
‘““The West Indian hurricanes arise,” says Dové, “at the 
inner edge of the zone of trade-winds N.E. in the so-called 
region of calms, where the air ascends and flows away in 
the upper strata in the direCtion opposite to that of the 
trade-wind. This renders it probable that the primary 
cause of the cyclone is the intrusion of a portion of this 
upper current into that which lies underneath it.* The 
latter part of this sentence is conjectural, but the former 
the geographical fact with which we have to do. Loomis 
says, ‘‘ The West Indian hurricanes generally originate 
near the equatorial limit of the trade-winds, where these 
winds are irregular between the latitude ro° and 20° N., 
and longitude 50° and 60° W. This is just the region of 
trade-wind interference, just the territory on which the over- 
leaping S.E. trade, deflected a little by the land-mass of 
Dove’s Law of Storms, p. 135. 
