1815.] On Dalton’s Theory of Chemical Composition. 375 
obtained, these relative weights may be determined with greater 
precision. 
Some objections, however, have been made to this explanation of 
the phenomena of chemical composition. 
i. It is said that we have no means of ascertaining or judging of 
the weight or the magnitude of an atoni of any element, and that . 
any supposed relative weight of their atoms must therefore be a 
mere hypothetical assumption, from which no satisfactory conclusion 
can be drawn. 
It is true we can never expect to produce any of these minute 
divisions, so as to ascertain their relative weights by balancing them 
separately in scales. But if we may be allowed to compare great 
things with small, may not the same objection be made to the 
manner in which the relative masses of the planets are determined ?, 
These are by their great magnitude as much as the ultimate divi- 
sions of chemical elements are by their extreme minuteness, beyond 
the reach of the ordinary means of comparison. ‘The means, how- 
ever, by which the relative masses of the heavenly bodies have been 
determined, are quite as satisfactory as if they had been weighed in 
scales. They are determined by the observed phenomena of the 
heavens, on the principle that these phenomena may be distinctly 
explained by supposing the masses, distances, and attractions, of the 
different bodies in question to bear certain relations to each other. 
And if the observed phenomena of chemical composition can be 
explained by supposing the weights of the ultimate divisions of che- 
mical elements to bear certain relations to each other, we may be 
equally well satisfied that such relations exist. 
2. But it has been said that the phenomena of chemical compo- 
sition require no such supposition, that we may with as much con- 
sistency suppose the ultimate divisions of all elements to be of equal 
weight, or that we may suppose their weights to bear any imaginable 
proportion to each other. Let us examine how far such suppositions 
are consistent with the observed phenomena. 
If we suppose the atoms of all elements to be of equal weight, we 
may suppose 28 atoms of carbon to be united to five of hydrogen in 
the composition of olefiant gas ; four of carbon to five of oxygen in 
carbonic oxide; and one of hydrogen to seven of oxygen in the 
composition of water. 
But in this way we should leave the agreement in the proportions 
observed by Mr. Dalton quite unaccounted for. And if the pheno- 
mena of chemistry are ever to be reduced into a system, like those_ 
of astronomy, surely such a series of remarkable agreements must 
be considered as a promising clue to lead to the true theory. 
We may indeed suppose 28 atoms of carbon to be united to 35 
of oxygen in carbonic oxide, and five of hydrogen to 35 of oxygen 
in the composition of water, and thus exhibit the same agreement 
which Mr. Dalton observed; but still we cannot show by these com- 
binations any reason for this agreement. 
Besides, if we attempt to form an idea of the position and 
