30 REPORT— 1867. 



to our present plan, the former are referred to two units of space and the latter to 

 one. But when the compounds of chloriue and tlie allied elements, with hydrogen, 

 are to he represented according to Sir B. Brodie's system, it at once becomes appa- 

 rent that some further hypothesis must he introduced if they are to be referred to 

 the same volume. When the quantity of hydrogen represented by the symbol a, 

 unites with chlorine, the product fills itwo units of space, and as, according- to the 

 fundamental hypothesis, a is indivisible, the question is to obtain some means of 

 expressing without fractions the quantity of hydrochloric acid which fills the unit 

 of space. This end Sir Benjamin attains by assuming that chlorine is itself a com- 

 poimd of hydrogen with an unknown element to which the symbol x is assigned; 

 clilorine being n;^',, and formed by three operations, one being hydrogen, and the 

 other two which are identical, result in the introduction into the. unit of space of 

 two quantities of a h^i^othetical substance x, whose weight is 17-25 : and according 

 to this view, when hydrogen and chloriue unite, the action is expressed by the 

 equation 



_ . ax., + a = 2ax. 



On precisely the same principle iodine, bromine, nitrogen, phosphorus, antimony, 

 and bismuth must alsoije hydrogen compounds. It is obvious therefore that Sir 

 Benjamin's system involves a very large amount of hypothesis ; for it assumes that 

 a considerable number of those substances hitherto regarded as elements are really 

 compounds. I do not imagine that much difficulty will be experienced by any 

 one in admitting the possibility of this, for I apprehend there is no chemist who 

 imagines those bodies which we call elements to be the ultimate constituents of 

 matter, or who doubts that the time, though still far distant, will come when they 

 may be resolved into simpler substances. But when we come to reduce the.se 

 specidations to a definite form, and seek to make them part of the science itself, it 

 becomes essential to subject them to a very close and searching scrutiny. 



In order to justify their assumption, it seems to me necessary either that they 

 should be supported by experimental evidence, or that they should afford the means 

 of tracing out unsuspected relations, and thus extending the bounds of the science, 

 or, at all events, that they should involve the minimum amount of hypothesis. 

 Now, as regards the first of these, it is unnecessary to observe that there "is not one 

 tittle of evidence to show that chlorine is a compound any more than hydrogen 

 itself. As far as extending the bounds of the science is concerned, we must look 

 for an answer to the future, and it may be expected that in the remaining parts of 

 the invesrigation, which it is to be hoped may soon be made public, it will be 

 shown how the method may be used for this puqiose ; but, in the meantime, I am 

 unable to see how it is to open up new fields of inquiry, and it is certain that it 

 leaves unexplained all those anomalies which are usually considered to be the weak 

 pointsof the existing system. Neither can it be asserte'd that the system involves 

 the minimum amount of hypothesis ; for, in point of fact, the assumption of the 

 compound nature of certain of the elements is rendered necessary by the funda- 

 mental h}i5othesis that a is indivisible. If it be assumed to be divisible, "tlie necessity 

 fin- holding those elements to be compound at once falls to the ground, and I confess 

 it appears to me that we should require very clear evidence of the advantages it 

 offers before we accept a hypothesis invoh-ing so many others. The question must 

 at best be considered as still sub judice, and the method is not lilcely to meet with 

 general acceptance tmtil it is supported by a much larger body of facts than those 

 we at present have. 



While Sir B. Brodie's theory is one from which the idea of atoms is excluded, it 

 is important to notice that it is by no means incompatiljle with th.em, and it even 

 appears to me that though it may suit our convenience to consider n.atter in rela- 

 tion to space only, the real subject of inquiry is not the unit of space, but the unit 

 of matter, and to it we must eventually come. If I hold, as I moFt xmdoubtedly 

 do, that the atomic theory of Diilton must sooner or later be abandoned, it is not 

 because I do not believe in the existence of a unit of matter. Whether we assume 

 it to be a hard spherical particle, a centre of force, or a vortex produced in a per- 

 fect ether, is another question ; but it seems evident that some kind of molecidar 

 hypothesis is indispensable for the explanation of physical phenomena, and it is 

 scarcely possible to doubt that some connexion must" exist between the chemical 



