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TEMSACTIONS OF THE SECTIONS. 



Section A.— MATHEMATICAL AND PHYSICAL SCIENCE. 

 •Pbesident of the Section — Professor G. H. Daewin, M.A.,LL.D., F.K.S., F.K.A.S. 



THURSDAY, SEPTEMBER 2. 

 The President delivered the fonowing Address : — 



A mebe catalogue of facts, however well arranged, has never led to any important 

 scientific generalisation. For in any suhject the facts are so numerous and many- 

 sided that they only lead us to a conclusion when they are marshalled by the light 

 of some leading idea. A theory is then a necessity for the advance of science, and 

 we may regard it as the branch of a living tree, of which facts are the nourishment. 

 In the struggle between competing branches to reach the light some perish, and 

 others form vigorous limbs. And as in a tree the shape of the young shoot can 

 give us hut little idea of the ultimate form of the branch, so theories become largely 

 transformed in the course of their existence, and afford in their tiu:n the parent 

 stem for others. 



The success of a theory may he measured by the extent to which it is capable 

 of assimilating facts, and by the smaUness of the change which it must undergo in 

 the process. Every theory which is based on a true perception of facts is to some 

 •extent fertile in affording a nucleus for the aggregation of new observations. And 

 a theory, apparently abandoned, has often ultimately appeared to contain an element 

 of truth, which receives acknowledgment hy the light of later views. 



It will, I think, be useful to avail myself of the present occasion to direct your 

 attention to a certain group of theories, which are stOl in an undeveloped and 

 somewhat discordant condition, but which must form the nucleus round which 

 many observations have yet to be collected before these theories and their descend- 

 ants can make a definitely accepted body of truth. If I am disposed to criticise 

 some of them in their actual form, I shall not be understood as denying the great 

 service which has been rendered to science by their formulation. 



Great as have been the advances of geology during the present century, we 

 have no precise knowledge of one of its fundamental units. The scale of time on 

 which we must suppose geological history to be dravra is important not only for 

 geology itself, but it has an intimate relation with some of the profoundest questions 

 of biology, physics, and cosmogony. 



We can hardly hope to obtain an accurate measure of time from pure geology, 

 for the extent to which the events chronicled in strata were contemporaneous is not 

 written in the strata themselves, and there are long intervals of time of which no 

 record has been preserved. 



An important step has been taken by Alfred Tylor, Croll, and others, towards 

 the determination of the rate of action of geological agents.' From estimates of 



> Geikie, Textbook of Geology, 1882, p. 442. 



