Manchester Memoirs, Vol. I. (1906), No. II. ii 



These three cases shew how widespread is behef in 

 this Law ; and they also shew that in these three cases at 

 least it is not valid. 



The difference between the expectation based on this 

 Law* and the accurate knowledge of what actually takes 

 place (which it is the business of Mendelian investigation 

 to supply), is the same as the difference between common 

 sense and science, and the same as the difference between 

 that which stands to reason and that which rests on 

 evidence. 



3 {U). Menders Law. 



I do not propose to discuss here the statement that 

 the time has not yet come when we are justified in 

 speaking of Mendel's Laiv, nor to enquire into the meaning 

 of this statement : the question I propose to answer is, 

 " What is the essential feature of that which is called 

 Mendelism by those who believe in it, and Mendelianism 

 by those who do not ? " 



I divide definitions of the Law into two primary 

 categories : — 



(i.) Suitable for those who desire to establish the 

 invalidity of the Law. 



(ii.) Suitable for those who wish to discover whether 

 Mendelism has helped us or is likely to help us 

 to attain to a more intimate knowledge of 

 heredity. 



There is no difficulty in finding a definition of the 

 first class : a very satisfactory one is one which binds the 

 Mendelian down to the Law exactly as enunciated, and 

 the description of the phenomena exactly as given by 

 Mendel himself If this is carefully done, no difficulty 



* Huxley must have been thinking of some such Law as this when he 

 made the remarkable statement that science was organised common sense. 



