180 THIRD RKPORT — 1833. 



On the suliject of lij'drometry ^ve were equally ignorant ; and 

 although the Italian collection had been published several 

 years previously, and was well known on the Continent, it was 

 not until Mr. Mann published an abstract of that collection 

 that we were at all aware of the state of the science abroad. 



Under these circumstances the author of this paper was in- 

 duced, in the year 1830, to undertake a series of experiments to 

 ascertain, 1st, The friction of water against the surface of a 

 cylinder, and discs revolving in it, at different depths and ve- 

 locities : from which it appeared, that with slow velocities the 

 friction approximated the ratio of the surfaces, but that an in- 

 crease of surface did not materially affect it with increased velo- 

 cities ; and that with equal surfaces the resistances approxi- 

 mated to the squares of the velocities. 



2ndly, To ascertain the direct resistances against globes 

 and discs revolving in air and water alternately : from which it 

 resulted, that the resistances in both cases were as the squares 

 of the velocities; and that the mean resistances of circular discs, 

 square plates, and globes of equal area, in atmospherical air, 

 were as under : 



Circular discs . . 25-180 MS 



Square plates . . 22'010 in air, . . 1 '36 in water. 



Round globes . . 10-627 0-75 



3rdly, That with circular orifices made in brass plates of 

 gJg-th of an inch in thickness, and having apertures of i, ^, f , y 

 of an inch respectively, under pressures varying from one to 

 four feet, the average coefficients of contraction were, 



for altitudes of 1 foot 0-619 



4 feet 0-621 



For additional tubes of glass the coefficient was,. 



for 1 foot 0-817 



4 feet 0-806 



4thly, That the expenditures through orifices, additional 

 tubes, and pipes of different lengths, of equal areas and under 

 the same altitude as compared with the expenditui-e through a 

 pipe of 30 feet in length, are as 

 1 : 3 for orifices, 

 1 : 4 for additional tubes, 

 1 : 3-7 for a pipe 1 foot in length, 



1 : 2-6 8 feet , 



1 : 2-0 4 , 



1 : 1-4 2 . 



5thly, That with bent rectangular pipes ^ an inch in diameter, 

 and 15 feet in length, the expenditures were diminished with 

 fourteen bends two thirds, as compared with a straight pipe. 



