CHEMICAL SCIENCE. 201 



very striking differences in others. But all these speculations take for 

 granted a principle, with which I must confess I think chemists have 

 allowed themselves to be far too easily satisfied, viz., that all the atomic 

 numbers are multiples of that of hydrogen. Not until these numbers are 

 determined with a precision approaching that of the elements of the plan- 

 etary orbits, a precision which can leave no possible question of a tenth 

 or a hundredth of a per cent., and in the presence of which such errors 

 as are at present regarded as tolerable in the atomic numbers of even the 

 best determined elements shall be considered utterly inadmissible, I think, 

 can this question be settled; and when such gigantic consequences so 

 entire a system of nature is to be based on a principle nothing short of such 

 evidence ought, I think, to be held conclusive, however seductive the theory 

 may appear. I do not think such precision unattainable, and I think I per- 

 ceive a way in which it might be attained, but one that would involve an ex- 

 penditure of time, labor, and money, such as no private individual could 

 bestow on it. If the phenomena of chemistry are ever destined to be reduced 

 under the dominion of mathematical analysis, it will, no doubt, be by a very 

 circuitous and intricate route, and in which at present we see no glimpse of 

 light. We should, therefore, be all the more carefully on the watch in mak- 

 ing the most of those. classes of facts which seem to place us, not indeed 

 within view of daylight, but at what seems an opening that may possibly 

 lead to it. Such are those in which the agency of light is concerned in mod- 

 ifying or subverting the ordinary affinities of material elements, those to 

 which the name of actino-chemistry has been affixed. Hitherto the more 

 attractive applications of photography have had too much the effect of dis- 

 tracting the attention from the purely chemical question which it raises ; but 

 the more we consider them in the abstract, the more strongly they force 

 themselves on our notice : and I look forward to their occupying a much 

 larger space in the domain of chemical inquiry than is the case at present. 

 That light consists in the undulations of an ethereal medium, or at all events 

 agrees better in the characters of its phenomena with such undulations, than 

 with any other kind of motion which it has yet been possible to imagine, is 

 a proposition on which I suppose the minds of physicists are pretty well made 

 up. The recent researches of Prof. Thomson and Mr. Joule, moreover, have 

 gone a great way towards bringing into vogue, if not yet fully unto accepta- 

 tion, the doctrine of a more or less analogous conception of heat. When we 

 consider now the marked influence which the different calorific states of 

 bodies have on their affinities the change of crystalline form effected in 

 some by a change in temperature the allotropic states taken on by some on 

 exposure to heat or the heat given out by others on their restoration from 

 the allotropic to the ordinary form (for though I am aware that Mr. Gore 

 considers his electro-deposited antimony to be a compound, I cannot help 

 fancying that at all events the state in which the antimony exists in it is an 

 allotropic one), when, I say, we consider these facts in which heat is con- 

 cerned, and compare them with the facts of photography, and with the 

 ozonization of oxygen by the chemical rays of the electric spark, and with 

 the striking alterations in the chemical habitudes of bodies pointed out by 

 Draper, Hunt, and Becquerel ; and when, again, we find these carried so far 

 that, as in the experiments of Bunsen and Koscoe, we find the amount of 

 chemical action numerically measuring the quantity of light absorbed it 

 seems hardly possible not to indulge a hope that the pursuit of these strange 

 phenomena may by degrees conduct us to a mechanical theory of chemical 



