252 SCIENCE IN SHORT CHAPTERS. 



dresses the President lias usually made a comprehensive 

 and instructive survey of the progress of the whole range 

 of science during the past year, and has dwelt more partic- 

 ularly on some branch which from its own intrinsic merits 

 has claimed special attention, or which his own special 

 attainments have enabled him to treat with the greatest 

 ability and authority. A few President's have, like Dr. 

 Huxley last year, taken up a particular subject only, and 

 have discussed it more thoroughly than they could have 

 done had they also attempted a general historical survey. 



Every President until 1871 has scrupulously kept in .view 

 his judicial position, and the fact that he 'is addressing, not 

 merely a few learned men, but the whole of England, if not 

 the whole civilized world. They have therefore clearly 

 distinguished between the established and the debatable 

 conclusions of science, between ascertained facts and mere 

 hypotheses, have kept this distinction so plainly before their 

 auditors that even the most uninitiated, could scarcely con- 

 found the one with the other. 



In Sir William Thomson's address this desirable rule is 

 recklessly violated. He tells 'his unsophisticated audience 

 that Joule was able " to estimate the average velocity of the 

 ultimate molecules or atoms" of gases, and thus determined 

 the atomic velocity of hydrogen "at 6225 feet per second 

 at temperature 60 degs. Fahr., and 6055 feet at the freezing 

 point;" that " Clausius took fully into account the impacts 

 of molecules upon one another, and the kinetic energy of 

 relative motion of the matter constituting an individual 

 atom;" and that " he investigated the relation between their 

 diameters, the number in a given space, and the mean 

 length of path from impact to impact, and so gave the 

 foundation for estimates of the absolute dimensions of 

 atoms." Also that "Loschmidt, in Vienna, had shown, 

 and not much later Stoney, independently, in England, 

 showed how to reduce from Clausius and Maxwell's kinetic 

 theory of gases a superior limit to the number of atoms in a 

 given measurable space." 



The confiding auditor follows the President through 

 further disquisitions on the " superlatively grand question, 

 what is the inner mechanism of an atom?" and a minute 



