SIE B. C. BEODIE ON THE CALCULUS OE CHEMICAL OPEEATIONS. 
55 
may be given for believing this to be possible : the one, of an abstract kind, derived 
from the fundamental property of chemical symbols given in the equation 
a% 2 =« + 2^, 
whence it may be argued that, as we can theoretically resolve a^ 2 into a and % and 
we are not justified in shutting our eyes to the possibility that the unit of chlorine may 
actually be resolved into a unit of hydrogen and two units of the (as yet) unknown ele- 
ment x- The argument is just, but the presumption thus raised is excessively slight ; 
for we are able to make (on any hypothesis) so very small a proportion of the vast 
number of chemical substances, the possible existence of which is similarly indicated to 
us, that we have no expectation, capable of being estimated, of making any one substance 
in particular. In short, the thing is possible ; but on these grounds alone we cannot 
expect to be able to do it. The second argument is of far greater weight. It may be 
put thus: — All persons would admit the validity of our conclusions if, having first 
detected the element thus latent in its compounds, we were able to verify our hypo- 
thesis by digging it out. % having been discovered, there would be but little doubt as 
to the existence of co and v. We have not got quite to this point, but nevertheless we 
are not so very far from it ; for we can show clearly that the application of the very same 
formal principles of reasoning to existing facts would have enabled us similarly to detect, 
prior to their isolation, the latent existence in their compounds of elements which have 
actually been isolated*. 
Were we able to conduct our chemical experiments only between certain fixed limits 
of temperature (let us say between 0° and 300° C.), a barrier would be placed upon our 
researches. We might still conduct innumerable experiments, but the science which 
resulted from them would be essentially different to our present chemistry. Between 
these limits of temperature the appearance of the element carbon in any system of 
chemical transformations is a rare phenomenon indeed ; and it is by no means difficult 
to place ourselves, by an effort of imagination, in the position of chemists who should 
have a very varied and extensive knowledge of the chemical properties of the compounds 
of carbon, and yet be totally unaware of the existence of that element. Let us imagine, 
then, some unknown world, some Laputa (devoted to philosophy) in which the chemistry 
* Chemists are placed in regard to the ideal elements •%, w , /3, v, and those combinations of them which 
cannot be resolved into our actual elemental bodies, in a very similar position to that occupied by astronomers 
(if I may venture on such a comparison) towards the planet Neptune prior to its detection by the telescope. 
The existence of the planet Neptune could be inferred, as a highly probable contingency, from the perturbations 
of the orbit of Uranus ; and yet this planet might have remained for ever unseen by man. So, too, the existence of 
the element % may he similarly inferred from the peculiar forms of chemical metamorphosis ; and yet this ele- 
ment may never be isolated as an independent reality. It may exist and exercise (so to say) an appreciable 
influence upon the movements of our system, and nevertheless lie far beyond the range of facts accessible to our 
methods of experiment. No scientific hypothesis can have any claim whatever upon our notice which is inca- 
pable of experimental verification (a truth too often forgotten in chemical speculations) ; but this verification 
may be a very tardy process, and involves numerous trials and numerous failures before in either sense (so as 
to enable us to deny or affirm the hypothesis) it is accomplished. 
