346 Professor J. Arthur Thomson [March 30, 



WEEKLY EVENING MEETING, 



Friday, March 30, 1900. 



Alfred B. Kempe, Esq., M.A., Treas. K.S., Vice-President, 

 in the Chair. 



Professor J. Arthur Thomson, M.A. 

 Facts of Inheritance. 



One of the distinctive features of the nineteenth century has been a 

 reduction in the number of supposed separate powers or entities — 

 the use of William of Occam's razor, in fact. " Caloric " was one of 

 the first to be eliminated, yielding to the modern interpretation of 

 " heat as a mode of motion ; " " Light " had to follow, when the un- 

 dulatory theory of its nature was accepted ; a specific " Vital Force " 

 is disowned even by the Neo-vitalists ; " Force " itself has become a 

 mere measure of motion ; and so on. In view of this progress 

 towards greater precision of phraseology, it cannot be a matter for 

 surprise that a biologist should affirm that to speak of the " Principle 

 of Heredity " in organisms is like speaking of the " Principle of 

 Horologity " in clocks. The sooner we get rid of such verbiage the 

 better for clear thinking, since heredity is certainly no power or force, 

 or principle, but a convenient term for the relation of organic or 

 genetic continuity which binds generation to generation. Ancestors, 

 grandparents, parents are real enough ; children and children's 

 children are also very real ; heredity is a term for the relation of 

 genetic continuity which binds them together. As for such a ques- 

 tion as this, " Is my grandfather's environment my heredity ? " it 

 is an offence against Queen's English as much as against scientific 

 phraseology ; it should probably read, " Have the structural changes 

 induced by external stimulus on my grandfather's body had any 

 effect on my inheritance ? " 



Another distinctive feature in scientific progress has been the 

 introduction of precise measurement. It is hardly too much to say 

 that in the development of natural knowledge, science begins where 

 measurement begins. And this is the case in regard to inheritance. 

 As long as we are content to say, " This child takes after his grand- 

 father," " This pigeon shows a throw-back to its rock-dove ancestry," 

 and so on, we may be making interesting remarks, but it is only 

 when we are able to give precise measurements of the amounts of 

 resemblance or difference that we make contributions of real import- 

 ance to that department of life-lore which deals with inheritance. 

 Or, perhaps, instead of measurement, which may be taken in too 



