192 ANNUAL OF SCIENTIFIC DISCOVERY. 



the lowest 257. These determinations were made in the spring 

 of 1870. A number of similar determinations were made in the 

 winter of 1870-71, by Mr. Henry B. Hill, Assistant in the Labora- 

 tory of Harvard College, the experiments being made on the air 

 in the college grounds. The amounts varied from 308 to 376 

 parts, the average amount being 337 parts in a million. Mr. 

 Pearson also determined the amount of carbonic acid in the air of 

 various (40) school-houses of the city of Boston, the experi- 

 ments being performed in the early spring before artificial means 

 of heating had been discontinued. He found amounts varying 

 from 773 to 1,992 parts in a million, the average amount being 

 1,470 parts. Second Annual Report of the Massachusetts State 

 Board of Health, Boston, 1871. 



ATOMIC THEORY. 



Prof. Roscoe, in his opening address as President of the Chemi- 

 cal Section of the British Association, alluding to our imperfect 

 knowledge of the fundamental laws which regulate chemical 

 actions, brought forward the discussion which took place last year 

 at the Chemical Society on the subject of the atomic theory, and 

 says: "The president (Dr. Williamson) delivered a very inter- 

 esting lecture, in which the existence of atoms was treated as 

 * the very life of chemistry.' Dr. Frankland, on the other hand, 

 states that he cannot understand action at a distance between 

 matter separated by a vacuous space ; and, although generally 

 granting that the atomic theory explains chemical facts, yet he is 

 not to be considered as a blind believer in the theory, or as un- 

 willing to renounce it if anything better presents itself. Sir B. 

 C. Brodie and Dr. Odling both agree that the science of chemis- 

 try neither requires nor proves the atomic theory ; whilst the for- 

 mer points out that the true basis of this science is to be sought 

 in the investigation of the laws of gaseous combination or the 

 study of the capacity of bodies for heat, rather than in commit- 

 ting ourselves to assertions incapable of proof by chemical 

 means. Agreeing in the main myself with the opinions of the 

 last chemists, and believing that we must well distinguish be- 

 tween fact and theory, I would remind you that Daltoii's. dis- 

 covery of the laws of multiple and reciprocal proportions, I 

 use Dr. Odling's word, as well as the differences in the power 

 of hydrogen replacement in chlorhydric acid, water, ammonia, 

 and marsh gas, are facts, whilst the explanation upon the as- 

 sumption of atoms is, as far as chemistry is concerned, as yet ad- 

 vanced, a theory. If, however, the existence of atoms cannot be 

 proved by chemical phenomena, we must remember that the 

 assumption of the atomic theory explains chemical facts as the 

 undulatory theory gives a clear view of the phenomena of light. 

 Thus, for instance, one of the most important facts and relations 

 of modern chemistry, which it appears difficult, if not impossible, 

 to explain without the assumption of atoms, is that of isomerism. 

 How, otherwise than by a different arrangement of the single 

 constituent particles, are we to account for several distinct sub- 



