A STUMBLE ON THE LAW OF GRAVITATION. 233 



for you have to do with people who will keep their 

 word. 



The fourth is a too manifest error in your book en- 

 titled the New Science of Artillery, in which you will 

 have it, at the fifth proposition of the first book, that no 

 body of uniform weight can traverse any space of time or 

 place by natural and violent motion mixed together; 

 which is most false, and contrary to all reason and natural 

 experience. The argument with which you prove it is 

 still more extraordinary than the answer you gave to the 

 bookseller. Do you not know that it is unsuitable? In 

 its descent a body moves with increased velocity, and in 

 forward progress it moves with diminishing speed, as we 

 see in the throwing of a stone, which, as it descends, 

 comes faster and faster to the earth, but when it left the 

 hand went more and more slowly, from which you may 

 draw other strange arguments in the said book, if you 

 have it in mind that men of sense are not to be contra- 

 dicted lightly. I shall be held excused, I hope, for con- 

 tradicting you, because, in treating of artillery, which 

 was little in your vocation, you exerted yourself to say 

 something notable, and you must not, for my rudeness, 

 think that I am like yourself and Messer Zuan Colle. 



I send you two questions with their solutions, but the 

 solutions shall be separate from the questions, and the 

 messenger will take them with him ; and if you cannot 

 solve the questions he will place the solutions in your 



