268 Obituary Notices of Fellows deceased. 



Watson, however, discusses the possible forms of the molecule, and 

 was the first to introduce the most general conception of it as a system 

 defined by n, generalised co-ordinates and corresponding momenta. In 

 the discussion of the relation of the Theory of Gases to Thermo- 

 dynamics, as then known, he made considerable advance on Boltz- 

 mann's work. Maxwell's hypothesis of the inverse fifth power he did 

 not give in extenso, probably not considering it a sufficiently good work- 

 ing hypothesis. It is noteworthy that he refused to accept, though he 

 did not deny, the extension of the e * law to intermolecular forces, 

 which is distinctly asserted by Boltzmann. 



He had the advantage, while preparing this work, of correspondence 

 with Maxwell on many of the points arising. 



In 1877, this time in partnership with Mr. S. H. Burbury, he 

 contributed the article " Molecule " to the " Encyclopaedia Britannica," 

 ninth edition. In this article the same theory of gases is explained in 

 outline as in Watson's own book, but the article contains likewise 

 some account of the Diffusion and Viscosity of Gases as deduced from 

 the Kinetic Theory, and a somewhat more extended discussion of the 

 ratio between the two specific heats, and the problems thereout 

 arising. 



In 1879, again with Mr. S. H. Burbury as colleague, he published a 

 treatise on the Application of Generalised Co-ordinates to the Dynamics 

 of a Material System (Clarendon Press). It was a work on abstract 

 dynamics. It contained a new definition, fundamental to the theory, 

 of the generalised component of momentum. Also a discussion of the 

 abstract theorems of Bertrand, Gauss, and Thomson, relating to 

 impulsive motion from rest, the two latter theorems being presented in 

 a new form. The theory of kinetic foci, and of least action in the 

 strict sense, given in this work was also in great measure new. 



Watson then, again in partnership with S. H. Burbury, published a 

 treatise on the Mathematical Theory of Electricity and Magnetism, of 

 which the first volume "Electrostatics " appeared in 1885, the second, 

 " Magnetism and Electrodynamics," in 1889. As stated in the Preface, 

 this treatise was intended rather as a commentary on Maxwell's great 

 work than as an original investigation. Maxwell cared little for 

 mathematics, except as interpreting experiment, or suggesting lines of 

 investigation. His mathematics, for this reason, presented many 

 difficulties to the student, and were even, in some cases, accused of being 

 inaccurate. Watson and his colleague endeavoured to clear up these 

 difficulties, and in some cases, though but seldom, departed consider- 

 ably from Maxwell's method. The work was completed before the 

 great extension was given to electrical science by Hertz, Rontgen and 

 other recent investigators. For this reason it did not anticipate 

 the great importance since given to the theory of electrons. 



