202 MEMOIR OF AUGUSTUS DE MORGAN. 



To Dean Peacock on his Marriage. 



7 Camden Street, Oct. 21, 1847. 



1847. MY DEAR SIR, This morning I found two cards for me at 



the College, which informed me of your marriage, of which I had 

 heard nothing. In fact, for anything I knew, you might have 

 been as confirmed a Benedict as any Pope of that name. But 

 owing to the practice which ladies have of not putting the name 

 they leave as well as the one they take, I had no guess who Mrs. 

 Peacock had been ; and the theory of probabilities does nothing 

 in the way of inferring the probable name which a bride quits, 

 having given that which she takes. So I resolved on writing 

 hearty congratulations and warm good wishes on the existing 

 a priori (or if you will have it that priors are out of question by 

 their vows, say a diaconiori) presumption that you were well able 

 to know what was good for yourself. But it so happened that 

 an Ely man saw the cards in my hand, and, as the phrase 

 goes, told me all about it; and I was enabled to conclude from 

 other evidence that I might just keep my good wishes, and put 

 good prophecies in their place. Take them both, however. As 

 to this practice of putting only one value of the variable on 

 wedding cards, I object to it altogether ; in fact, I denounce it, 

 and will prove my objection good. I suppose 110 one will deny 

 that the cards represent the instant of the ceremony at which 

 the contract becomes indissoluble ; for before that moment the 

 announcement would be presumptuous, and to suppose that any 

 time elapses after it would be to suppose that a man takes that 

 time to consider whether he will acknowledge his marriage, 

 which is absurd. This being granted, let A B represent the 

 duration of the lady's life, and let M be that moment of the 



ceremony at which the contract becomes indissoluble. Let the 

 lady's name during A M be Selwyn, and during M B Peacock ; 

 then, because by common courtesy a lady is not a discontinuous 

 fraction, it follows that what is true up to the limit is true at 

 the limit, therefore at the moment M her name is Selwyn. But 

 for a similar reason her name at the same moment is also 

 Peacock ; therefore at the instant M she has both names, whence 

 both ought to appear on the wedding cards. Q.E D. 



I have your books on arithmetic in safety and memory, and 

 am only waiting to return them till I have put a copy of my 



