OF ARTS AND SCIENCES. Ill 



peculiarities of individuals could not be perpetuated as races 

 or varieties of men, as well as they now are of domestic animals. 

 According to the nature of the transmitted peculiarity, such 

 races would either be multiplied indefinitely, or the race would 

 die out and disappear. 



The great obstacle and safeguard against the transmission of 

 such diseases consists in the crossing of the race or breed. 

 Every cross effected with a healthy stock reduces the liability 

 one half, and every second cross reduces it to one quarter, and 

 so on. If it were otherwise, certain races would become ex- 

 tinct. There is probably no individual in this room, who does 

 not inherit from some of his ancestors a title to phthisis or gout 

 or insanity. Yet the great dilution or weakening of this title, 

 under repeated crosses, renders the predisposition inconsider- 

 able and ineffectual. 



Mr. Ritchie exhibited a quantity of liquefied nitrous oxide, 

 condensed by a very powerful pump, of his own contrivance, 

 and exhibited the instantaneous freezing of mercury in the 

 liquid, while charcoal burned with vivid ignition, as in oxygen 

 gas, at its surface. 



The President read the following letter from the venerable 

 Josiah Quincy. 



To Jacob Bigelow, M. Tt., President of the American Academy of 

 Arts and Sciences. 



Sir, — I shall be obliged if the Academy will so far deviate from 

 their usual practice as to anticipate their regular time of meeting in 

 February next, and, instead of the 12th, assemble at my house on 

 the evening of the 4th of that month, on which day I enter my nine- 

 tieth year. 



The occasion is peculiar, and not likely soon to recur again, or to be 

 drawn into a precedent. To me " the silver cord is not yet loosed," 

 though much frayed and life-worn, and the favor will be to me a grati- 

 fication and rejuvenescence. 



With perfect respect, I am yours, &c. 



Josiah Qdinct. 



Boston, January 8, 1861. 



