On Mr. Davy’s Hypothesis. 227 
and obtained a series of irregular polygons, the trace of 
which indicates the successive intersections of the surface 
of the soil by horizontal planes raised one-metre above each 
other. 
These polygons, more or less distant from each other as 
the slope of the ground is more or less rapid, indicate to 
the eye in the most palpable and rigorous manner, the in- 
clination of the hillocks which run parallel with the banks 
of the Seine, as well.as the factitious mounds which we 
remark in the bottom of the valley, and which we have al- 
ready mentioned. 
The general survey of the city of Paris was finished in 
two years. It required operations in detail of a.most mul- 
tifarious kind; and I have no doubt that, by following the 
order and course which J have pointed out in another me- 
moir *, we shall in a few years bein possession of results 
equally satisfactory with respect to the general survey of 
France. 
XL.—Olservations and Experiments concerning Mr. Davy’s 
Hypothesis of Electro-chemical Affinity.—By M.Dono- 
van, Esq. 
Mz. Davy’s hypothesis of the identity of chemical and 
electric attraction, although ably supported by a variety 
of strong facts, ingenious reasonings, and happy illustra- 
tions, is not confirmed by the concordance of known phe- 
nomena. Between these powers so many differences are 
observable, the one is so often produced where the other 
can scarcely be supposed to operate, or, according to what 
is known, onght to operate differently, that we cannot with 
any degree of confidence rest on the assumption of their 
similarity ; the less so, whew it is reflected that the whole 
is supported by probabilities only, without even the pro- 
fession of a single proof. However truly philosophical 
may be the design of referring all the operating energies of 
nature to one great universal cause; yet must we proceed 
with caution, and not be misled to pronounce causes iden- 
tical before we are convinced of their real connexion. The 
limited perceptions of man do not allow him to survey the 
chain of causes at one steady comprehensive view. There 
must at length be a break ; and when he loses sight of the 
connexion, he can no longer pronounce upon identity. 
The reasonings in the following pages rest not on a hy- 
* Journal des Mines, tom. xvii p. 297. 
: P2 pothetical 
