A HISTORY OF SCIENCE 



on the whole rather more so than those of the other 

 two that we give them in part here: 



"i. If a hard body should strike against a body 

 equally hard at rest, after contact the former will rest 

 and the latter acquire a velocity equal to that of the 

 moving body. 



" 2. But if that other equal body be likewise in mo- 

 tion, and moving in the same direction, after contact 

 they will move with reciprocal velocities. 



"5. A body, however great, is moved by a body 

 however small impelled with any velocity whatsoever. 



" 5. The quantity of motion of two bodies may be 

 either increased or diminished by their shock ; but the 

 same quantity towards the same part remains, after 

 subtracting the quantity of the contrary motion. 



" 6. The sum of the products arising from multiply- 

 ing the mass of any hard body into the squares of its 

 velocity is the same both before and after the stroke. 



" 7. A hard body at rest will receive a greater quan- 

 tity of motion from another hard body, either greater 

 or less than itself, by the interposition of any third 

 body of a mean quantity, than if it was immediately 

 struck by the body itself ; and if the interposing body 

 be a mean proportional between the other two, its action 

 upon the quiescent body will be the greatest of all." 10 



This was only one of several interesting and impor- 

 tant communications sent to the Royal Society during 

 his lifetime. One of these was a report on what he 

 calls " Pneumatical Experiments." "Upon including 

 in a vacuum an insect resembling a beetle, but some- 



222 



