6 REPORT— 1901. 



from the influence of the moment and to avoid, even if it were desirable to 

 avoid, the inclination to look backward from the standpoint of to-day. 



Two years ago Sir Michael Foster dealt with the work of the century 

 as a whole. Last year Sir William Turner discussed in greater detail 

 the "Towth of a single branch of science. A third and humbler task 

 remains, viz.. to fix our attention on some of the hypotheses and assump- 

 tions on which the fabric of modern theoretical science has been built, and 

 to inquire whether the foundations have been so ' well and truly ' laid 

 that they may be trusted to sustain the mighty superstructure which is 

 being raised upon them. 



The moment is opportune. The three chief conceptions which for many 

 years have dominated physical as distinct from biological science have 

 been the theories of the existence of atoms, of the mechanical nature of 

 heat, and of the existence of the ether. 



Dalton's atomic theory was first given to the world by a Glasgow pro- 

 fessor—Thomas Thomson— in the year 1807, Dalton having rommunicated 

 it to liini in 1804. Rumford's and Davy's experiments on the nature 

 of heat were published in 1798 and 1799 respectively; and the cele- 

 brated Bakerian Lecture, in which Thomas Young established the 

 undulatory theory by explaining 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-countrymen, one of whom — Sir Benjamin Thompson, 

 Count Ilumford — preferred exile from the land of his birth to the loss of 

 his birthright as a British citizen. 



*&' 



Douhts as to Scientific Theories. 



It is well known that of late doubts have arisen as to whether the 

 atomic theory, with which the mechanical theory 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, addressini; a congress of physicists 

 n 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 delixered an 

 attack of great power on many positions which eminent scientific men 

 have occupied ; 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 diffi- 

 culties 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 compara- 

 tively little reference to the ether, and we may also at first confine our 

 a,ttention to inanima,te objects. 



