38 REPORT— 1879. 



history and present state of a science lias for its main aim to enumerate 

 the various authors and to point out their relative weight, and this has 

 been very well done in several British Association Reports, some of which 

 are nearly as old as the British Association. 



' There are some branches of science whose position with respect to 

 the public, or else to the educational interest, is such that treatises or 

 text-books can be published on commercial principles, either as books to 

 be read by the free public, or to be got up by the school public. 



' There is little encouragement, however, for a scientific man to write 

 a treatise so long as he can, with much less trouble, produce an original 

 memoir, which will be much more readily received by a learned society 

 than the treatise would have been by a publisher. 



' The systematisation of science is therefore carried on under difficulties 

 when left to itself ; and I think that the experience of the British Asso- 

 ciation warrants the belief that its action in asking men of science to 

 furnish reports has conferred benefits on science which would not other- 

 wise have accrued to it. 



' There are so many valuable reports in the published volumes that I 

 shall indicate only a few, the selection being founded on the direction of 

 my own work rather than on any less arbitrary principle. 



' First, when a branch of science contains abstruse calculations as well 

 as interesting experiments, it is desirable that those who cultivate the 

 experimental side should be conscious that certain things have been done 

 by the mathematicians. The matter to be reported on in this case is not 

 voluminous, but it is hard reading, and those who are not experts require 

 a guide. 



' Thus, Professor Challis in 1834 gave a most useful report on the 

 mathematical investigations by Young, Laplace, Poisson, and Gauss on 

 Capillary Attraction, and Professor Stokes in 1862 reports on Theories- 

 of Double Refraction. This report may, indeed, be accepted as an instal- 

 ment of the treatises which, if the desire of the scientific world were law, 

 Professor Stokes would long ago have written. It is meant, no doubt, as 

 a guide to other men's writings, but it is intelligible in itself without 

 reference to those writings. Such a report is a full justification of the 

 existence of the British Association, if it had done nothing else. 



' Another type of report is that of Professor Cayley on Dynamics 

 (1857 and 1862). This seems intended rather as a guide in reading the 

 original authors than as a self-interpreting document, though, of course, 

 besides the criticism and the methodical arrangement, there is much 

 original light thrown on the mass of memoirs discussed in it. It will be 

 many years before the value of this report will be superseded by treatises. 



' The Report of the Committee on Mathematical Tables deals with a 

 subject which, though not so abstruse, is larger and drier than any of the 

 preceding. It is, however, a most interesting as well as valuable report, 

 and supplies information which would never have been printed unless the 

 British Association had asked for the report, and which never would 

 have been obtained if the author of the report had not been available. 



' There are several other reports which are not mere reports, but 

 rather original papers preceded by a historical sketch of the subject. No 

 special encouragement is needed to get people to write reports of this 

 kind.' 



Professor Stokes thus expresses himself on the subject : — 



' It seems to me that reports on the progress of science may be of 



