314 MEMOIR OF AUGUSTUS DE MORGAN. 



1862. able or unimaginable. I take a right to affirm the conception of 

 D such that 



A : B::C : D 



The notion of ratio is a fundamental thing, not dependent on, 

 though only definitely expressible by number. A person who 

 cannot count, and who does not even know that language can 

 turn multitude into number, has the idea of ratio, relative mag- 

 nitude. He sees, feels, and knows that if A be the house, B is 

 too small for the chimney, and C too large. 1 I claim the exist- 

 ence of D, so that A : B as C : D is a concept. 



This being premised, then I have the infinitely small part of 

 any magnitude, and of that again, &c. For instance, if dx : x :: 

 a pint pot : all space, dx is an infinitely small part of x. 



All this I mean to develop and fight for. So with kind 

 regards to Lady Herschel and the next generation, 



Yours sincerely, 



A. DE MORGAN. 



To Sir J. Herschel. 



91 Adelaide Road, Aug. 15, 1862. 



MY DEAR SIR JOHN, Many thanks for the dialogue. 2 From 

 the parties to the dialogue I deduce the equation 



mogenes + mione_ , , 



What a quantity of arguable propositions ! I cannot see how 

 you deduce your account of Descartes. As to at'ems I spell 

 the name thus, considering it as a challenge to attack them, and 

 make your boast of it I suspect that if you look back into the 

 world a thousand years hence you will find the remote posterity, 

 as we call it, fiddling away at the creatures, and knowing about 

 what we do. 



I have often thought of the minimum of extension en- 

 dowed with attraction, &c., and adjusting his accounts with 

 f (10 )i,ooo,ooo,ooo]. (10 ) 1,000,000,000 brethren instantaneously. It is 

 a wonderfully fine hypothesis for expressing what we see and 



1 A rough sketch of a house, with a too small chimney on one side 

 and a too large one on the other. 



2 Dialogue on Atoms, by Hennogenes and Hermione. Private 

 circulation. 



