428 



SCIENCE. 



[N. S. Vol. XIV. No. 351. 



Dalton's atomic theory was first given to 

 the world by a Glasgow professor— Thomas 

 Thomson— in the year 1807, Dalton having 

 communicated it to him in 1804. Eum- 

 ford's and Davy's experiments on the na- 

 ture of heat were published in 1798 and 

 1799 respectively ; and the celebrated Ba- 

 kerian Lecture, in which Thomas Young 

 established the undulatory theory by ex- 

 plaining the interference of light, appeared 

 in the Philosophical Transactions in 1801. 

 The keynotes of the physical science of the 

 nineteenth century were thus struck, as the 

 century began, by four of our fellow-coun- 

 trymen, one of whom — Sir Benjamin 

 Thompson, Count Rumford — preferred ex- 

 ile from the land of his birth to the loss of 

 his birthright as a British citizen. 



DOUBTS AS TO SCIENTIFIC THEORIES. 



It is well known that of late doubts have 

 arisen as to whether the atomic theory, 

 with which the mechanical theorj^ of heat 

 is closely bound up, and the theory of the 

 existence of an ether have not served their 

 purpose, and whether the time has not 

 come to reconsider them. 



The facts that Professor Poincare, ad- 

 dressing a congress of physicists in Paris, 

 and Professor Poynting, addressing the 

 Physical Section of the Association, have 

 recently discussed the true meaning of our 

 scientific methods of interpretation ; that 

 Dr. James Ward has lately delivered an 

 attack of great power on many positions 

 which eminent scientific men have occu- 

 pied ; and that the approaching end of the 

 nineteenth century led Professor Hseckel to 

 define in a more popular manner his own 

 very definite views as to the solution of the 

 ' Riddle of the Universe,' are perhaps a 

 sufficient justification of an attempt to lay 

 before you the difficulties which surround 

 some of these questions. 



To keep the discussion within reasonable 

 limits I shall illustrate the principles under 



review by means of the atomic theory, with 

 comparatively little reference to the ether, 

 and we may also at first confine our atten- 

 tion to inanimate objects. 



THE CONSTRUCTION OP A MODEL OF NATURE. 



A natural philosopher, to use the old 

 phrase, even if only possessed of a most 

 superficial knowledge, would attempt to 

 bring some order into the results of his ob- 

 servation of nature by grouping together 

 statements with regard to phenomena which 

 are obviously related. The aim of modern 

 science goes far beyond this. It not only 

 shows that many phenomena are related 

 which at first sight have little or nothing 

 in common, but, in so doing, also attempts 

 to explain the relationship. 



Without spending time on a discussion 

 of the meaning of the word ' explanation,' 

 it is sufficient to say that our efi^orts to es- 

 tablish relationships between phenomena 

 often take the form of attempting to prove 

 that, if a limited number of assumptions 

 are granted as to the constitution of matter, 

 or as to the existence of quasi material 

 entities, such as caloric, electricity and the 

 ether, a wide range of observed facts falls 

 into order as a necessary consequence of the 

 assumptions. The question at issue is 

 whether the hypotheses which are at the 

 base of the scientific theories now most 

 generally accepted are to be regarded as 

 accurate descriptions of the constitution of 

 the universe around us, or merely as con- 

 venient fictions. 



Convenient fictions be it observed, for 

 even if they are fictions they are not use- 

 less. From the practical point of view it 

 is a matter of secondary importance whether 

 our theories and assumptions are correct, 

 if only they guide us to results which are 

 in accord with facts. The whole fabric of 

 scientific theory may be regarded merely 

 as a gigantic ' aid to memory ' ; "as a means 

 for producing apparent order out of dis- 



