a Tat eS i a SR ne Ot» Seek eee ee eae aa 
_ ” 
Set et ct ket OL 
a 
ing explanation. 
P. E. Chase on Terrestrial Magnetism. 379 
‘ward or westward, in accordance with the theory of M. Dov 
The disturbance of the ether, dependent upon the relative at- 
t 
_ Having thus ascertained the causes and directions of the prin- 
cipal normal currents, the ordinary theory of winds enables us 
a centre of polarity with an attractive energy that disturbs the 
atmospheric equilibrium, tending to produce wind and rain. I 
the disturbance is confin limited area, there is a well- 
known cyclonic tendency, the portion of the eddy which is near- 
est the equator generally flowing eastward. Mr. Galton™ has 
ingeniously shown that, in descending cyclones, the direction 
may be reversed, and I should expect a similar reversal to be of 
frequent occurrence in the neighborhood of some of the power- 
ful ocean-currents, at points where they tend to produce back- 
ward eddies. Such points are found midway between the Sand- 
wich Islands and California, about 85° west of Chili, near the 
west coast of New Holland, in the Indian Ocean, northeast of 
Madagascar, and in other places. 
The effect of ocean-currents in producing cyclones, and di- 
recting their course, is well illustrated by the repeated observa- 
tions that have been made in the Gulf Stream. Prof. Lesley’s 
_ Mteresting account of the series of storms encountered by t 
Canada on her one hundredth voyage," exhibits the natural 
Consequences of the friction of two belts of air at different tem- 
peratures, moving in opposite directions. The warm air over 
the Gulf Stream, and the cold air over the Arctic currents that 
w nearer to the American continent, are both borne very 
Nearly in their normal directions, but with the approach of win- 
ter their parallelism becomes almost vertical, the cold belt be- 
comes wider from its encroachment upon the land, and the vor- 
that arise from their concurrence are frequently brought 
own to the surface of the ocean, instead of taking place in the 
a regions of the air, as they usually do during summer. 
,, While sudden, violent tempests that are occasioned by local 
listurbances over a limited area, are almost necessarily cyclonic, 
am inclined to adopt Espy’s theory with regard to long storms, 
hat usually “the wind will blow in toward a line rather than 
Oward a point;’’ and in favor of this hypothesis, as well as of 
he periodicity of weather-changes, I would suggest the follow- 
- % Phil. Mag., Sept. 1863. 
%* Proc. Amer. Philos. Soc., ix, 361. 
