524 



SCIENCE. 



[N. S. Vol. XVIII. No. 400. 



are quite dogmatic in their utterances; 

 some only seek to evade the theory, without 

 going to the extreme of an absolute denial; 

 and still others, more timid, assume an 

 apologetic tone, as if the atom were some- 

 thing like a poor relation, to be recognized 

 and tolerated, but not to be encouraged too 

 far. Now caution is a good thing, if it is 

 not allowed to degenerate into indecision; 

 when that happens, mental obscurity is 

 the result. In science we must have 

 intellectual resting-places; something to 

 serve as a foundation for our think- 

 ing; something concrete and tangible 

 in form. No theory is immune against 

 hypercriticism ; none is absolute and 

 final; with these considerations borne 

 in mind we may ask whether a doc- 

 trine is serviceable or not, and we can use 

 it without fear. When we say that matter, 

 as we know it, behaves as if it were made 

 up of very small, discrete particles, we do 

 not lose ourselves in metaphysics, and we 

 have a definite conception which can be 

 applied to the correlation of evidence and 

 the solution of problems. Objections count 

 for nothing against it until something bet- 

 ter is offered in its stead, a condition which 

 the critics of the atomic theory have so far 

 failed to fulfil. They give us no real sub- 

 stitute for it, no other working tool, and so 

 their objections, which are too often meta- 

 physical in character, command little seri- 

 ous attention. Criticism is useful, just so 

 far as it helps to clarify our thinking; 

 when it becomes a mere agent of destruc- 

 tion it loses force. 



Broadly speaking, then, the modern 

 critics of the atomic theory have shaken it 

 but little. Still, some serious attempts 

 have been made towards forming an alter- 

 native system of chemistry, or at least a 

 system in which the atom shall not avow- 

 edly appear. The most serious, and per- 

 haps the most elaborate of these devices 



was that brought forward in 1866 by Sir 

 Benjamin Brodie,* in his 'Calculus of 

 Chemical Operations,' which he defended 

 later (1880) in a little book entitled 'Ideal 

 Cheraistiy. ' In this curious investigation, 

 Brodie tries to avoid hypotheses and to 

 represent chemical acts as operations upon 

 the unit of space by which weights are gen- 

 erated. This notion is a little difficult to 

 grasp, but Brodie 's procediire was per- 

 fectly legitimate. His one fundamental 

 assumption is that hydrogen is so generated 

 by a single operation, and upon this he 

 erects a system of symbols which, treated 

 mathematically, lead to some remarkable 

 conclusions. For instance, chlorine, 

 bi-omine, iodine, niti-ogen and phosphorus 

 become compounds of hydrogen with as 

 many unknown or 'ideal' elements, which 

 no actual analysis has yet identified. That 

 is, the known phenomena of chemistry 

 seem to be less simply interpreted by 

 Brodie 's calculus than in our commonly 

 accepted theories, and certain classes of 

 phenomena are not considered at all. It 

 is true that Brodie never completed his 

 woi-k, but it is not easy to see how his nota- 

 tion and reasoning could have accounted 

 for isomerism, much less for the facts 

 which stereochemistry seeks to explain. 



Just here A?e find the prime difficulty of 

 all attempts to evade the atomic theory. 

 Up to a certain point we can easily dis- 

 pense with it, for we can start with the fact 

 that every element has a definite combining 

 number, and then, without any assumptions 

 as to the ultimate meaning of these con- 

 stants, we can show that other constants 

 are intimately connected with them. So 

 far, Ave can ignore the origin of the so- 

 called atomic weight; but the moment we 

 encounter the facts of isomerism or chem- 

 ical structure, and of the partial substitu- 

 tion of one element by another, oui- troubles 



" Phil. Trans., 1866. A .second part in 1877. 



