574 PHILOSOPHICAL TRANSACTIONS. [anNO ITTl. 



strike perpendicularly against the middle of the outermost of the silks, and by 

 breaking through them to lose part of its motion. If the pieces of silk be of 

 equal strength, the same degree of force will be required to break each of them; 

 but the time in which each piece of silk resists will be so much shorter as the 

 globe is swifter, and the loss of n>otion in the globe consequent upon its break- 

 ing through each silk, and surmounting the resistance thereof, will be propor- 

 tional to the time in which the silk opposes itself to the globe's motion ; inso- 

 much that the globe by the resistance of any one piece of silk will lose so much 

 less of its motion as it is swifter. But on the other hand, by how much swifter 

 the globe moves, so many more of the silks it will break through in a given 

 space of time; whence the number of the silks which oppose themselves to 

 the motion of the globe in a given time, being reciprocally proportional to the 

 effect of each silk upon the globe, the resistance made to the globe by these 

 silks, or the loss of motion the globe undergoes by them in a given time, will 

 be always the same. 



Now if the tenacity of the parts of fluids observes the same rule as the cohe- 

 sion of the parts of these silks; namely, that a certain degree of force is 

 required to separate and disunite the adhering particles, the resistance arising 

 from the tenacity of fluids must observe the same rule as the resistance of the 

 silks. And therefore, in a given time the loss of motion a body undergoes 

 in a fluid by the tenacity of its parts, will, in all degrees of velocity, be the 

 same; or in other words, that part of the resistance of fluids which arises from 

 the cohesion of their parts, will be uniform. 



An Account of the Falls of the River Niagara^ taken at Albany ^ Oct. 10, 1721, 

 from M, BorassaWf a French Native of Canada. By the Hon. Paul Dudley, 

 F.R.S. N°37i, p. 69. 



The falls of Niagara are formed by a vast ledge or precipice of solid rock, 

 lying across the whole breadth of the river, a little before it empties itself into, 

 or forms the lake Ontario. 



M. Borassaw says, that in spring 1722, the governor of Canada ordered his 

 own son, with three other officers, to survey the Niagara, and take the exact 

 height of the cataract, which they accordingly did with a stone of half a hundred 

 weight, and a large cod-line, and found it on a perpendicular no more than 26 

 fathoms, vingt et six brass. 



This differs very much from the account Father Hennepin has given of that 

 cataract; for he makes it 100 fathoms, and our modern maps from him, as I 

 suppose, mark it at 60O feet; but I believe Hennepin never measured it, and 

 there is no guessing at such things. , , 



