28 — Hints for the Formation of a Theory of the Earth. os 
i fay the fame thing of thofe fituated to the weft. If this rea~ 
foning be juft, the needle ought not to vary by the action of 
the folar heat, but when this heat diminithes the magnetic 
foree of the ferruginous parts fituated to the north of the ~ 
needle, more than that of the parts fituated to the fouth, or | 
reciprocally. ‘* 7" 
-To determine this curious queftion, it would be lain 
to make choice of two oppofite coafts, and directed: almoft 
eaft and weft from the magnetic meridian; fuch as the coat - 
of Provence to the fouth, and that of Normandy to the north ; 
to eftablifh two compafies well fufpended, fuch as thofe of 
M. Conlomb, one*to the fouth, at Antibes for example, 
and the-other to the north, near Cape de La Hogue; and to 
fee whether their diurnal variations did not proceed in a con= 
trary direction: that is to fay, whether that at Antibes, 
having the continent to the north, and only fea to the fouth, 
Ww dull. not decline, in.the morning, towards the weft, as that 
of Mr. Canton did; and whether that of La Hogue, having 
the continent to the fouth and fez to the iH would not, 
at the fame ‘time, decline to the eaft. Myr. Canton, indeed; 
who made thefe obfervations at London, had, to the north 
of his magnetic horizon, the greater part of England and all 
Ireland; and thus he muft bave had the variation weft in 
the morning and eaft in the evening, as he oblerved it; for 
it is certain that the fea preferves the land, which it covers; 
from the a@ion of the fun; and that thus the attraction of 
that land ought not to vary by the heat which emanates 
from that luminary. 
By carefully repeating and varying thefe obfervations, in 
places chofen with difcernment, we fhall be able to decide 
whether the recular diurnal variation depends upon a general 
“caufe, the action of which, however, is fufceptible of being 
fufpended or difturbed by local caufes; or whether we are to 
Lelieve, on the contrary, as M. Van Swinden does, that the 
diurnal variation is not a cofmic phenomenon, or that it does 
not depend on a general caufe inherent in the globe, and 
which every where acts according to the fame law. 
gy. Is there properly any action of the maguetic fluid on 
“the electric fluid? or is there, between thefe two fluids, only 
a refemblance of properties, or in their manner of action? 
- : £0. Is 
