31 



on these subjects relating to sexual distinctions* 

 But I feel the consequences of my resolution 

 the dread of offering examples, has rendered my 

 argument somewhat dubious. Brevis esse laboro 

 obscurusjio. 



I remain, &c. 



LETTER VI. 



SIR, 



You next proceed to investigate a very in- 

 teresting and important question, viz. whether 

 different kinds of men were originally created; 

 or whether we are to account for the diversities 

 which exist amongst mankind by the opera- 

 tions of subsequent physical and moral causes, 

 On the first supposition, as you remark, there 

 would be different species of the human race ; 

 whereas on the latter, they will form only dif- 

 ferent varieties of the same species. 



It is your next endeavour to shew that this 

 question must be exclusively determined by the 

 principles of physiology, independent of all 

 argument d priori, and of all national and his- 

 torical traditions. You then attempt to ridi- 

 cule those " regula fhilosophandi" which 

 were laid down by Newton,, and which would 



