$23 Observations and Experiments concerning 
pothetical assumption of two electric fluids, of one, or of 
none. In pursuing every investigation, we must reason on 
doubtful points by the assistance of those that are certainly 
known on the subject. That of this power, whatever be 
its nature, there exist two modifications, each of which 
has a strong tendency to approach the other to an insensi- 
ble distance, is proved beyond the possibility of doubt ; 
proved by the only means of decision in any matter; namely, 
the evidence of the senses. Jt is proved by no less a cer- 
tainty, that similar modifications have a tendency to recede 
from each other; and that where the dissimilar powers are 
at hberty to come into contact, they effect a mutual change 
which deprives each of its relative properties. These are 
all the postulates necessary to the following reasonings ; 
and it is of no consequence what expressions are used, 
nor whether positive electricity be considered as plus, and 
negative as minus ; nor whether doth are merely properties 
of matter, and not the agency of any fluid sui generis. The 
facts are indisputable, notwithstanding the insufficiency of 
language. But as the language of the hypothesis which 
supposes the existence of two, fluids is most easy of ex- 
pression, it shall be hereafter adopted. 
Mr. Davy has stated his opinion, that the effects attri- 
buted to a certain force called affinity, exerting its energy 
between the ultimate particles of heterogeneous matter, may 
be no more than the operations of electricity; and thinks 
that all the phenomena of affinity ought to happen con- 
formably to the known principles of electricity. 
He supposes that combined bodies are in differently elec- 
trical states: that acids and oxygen are in the negative 
state; that earths, alkalies, metals, oxides and inflammables 
are in the positive state: that the attraction of these dif- 
ferent powers is the force which sustains these substances 
in combination. J 
He illustrates such a combination by the example of 
Beccaria’s glass plates, differently electrified, which cohere 
with great force; and adds, that $ different particles in 
combining must be still supposed to preserve their peculiar 
states of energy.” 
He instances a variety of substances, as metals, acids and 
alkalies, which by a few contacts become electrical in dif- 
ferent states. 
Mr. Davy lastly supposes that artificial electricity effects 
the decomposition of those compounds, by attracting the 
éifferent and by repelling the similar power. 
Mr. Davy, it is plain, sets out with two assumptions. 
. Ist. That 
