550 



HYDRODYNAMICS. 



Resistance that the part of the resistance R is almost the same in 

 '-^"-^Z- '' as ' n water ! ft"" sine* this part arises merely from 

 " nr " the inertia of the particles, it ought in different fluids 

 to be proportional to their density. 



Coulomb intended, in a second memoir, to determine 

 numerically the value of the part of the resistance pro- 

 portional to the square of the velocity ; and to ascertain 

 the resistance of globes, of pallets, of convex and con- 

 cave surfaces ; and also the difference between the re- 

 sistance of a floating body and one entirely submerged ; 

 in consequence of his having found, that in slow mo- 

 tions the submerged body suffered a much less degree 

 of resistance. We have to regret, however, that Cou- 

 lomb did not live to complete these valuable researches. 

 He died on the 3d August 1806, in the 70th year of 

 his age ; and left behind him the reputation of being 

 one of the most able and original natural philosophers 

 of the age in which he lived. 



5. Account of the Experinients of the Society for the 

 Advancement of Naval Architecture. 



When the same body had prows differently inclined, 

 the following results were obtained. of 



Inclination of the 

 Prows. 

 44' 10" 

 28 

 28 



9 

 14 

 19 

 30 

 90 



40 



15 











Friction. 

 30.67 

 35.34 

 41 .71 

 51.44 



148.25 



Experi- 

 ments of 

 the Society 

 of Naval 

 Architec- 

 ture. 



WE regret that our limits will only permit us to lay 

 before our readers some of the results of these excellent 

 experiments. 



The following experiments were made with a sur- 

 face of 40 square feet, moving in its own direction with 

 different velocities. 



Velocities in Nautical 

 Miles per hour. 



1 



2 



4 

 6 



8 



Friction in 

 Pounds. 



0.563 



1.992 



6.643 



12.839 



19.856 



The Society likewise found, that the direct resistance 

 varied in a ratio a little greater than that of the square 

 of the velocity, being proportional to V 2 - 106 . A body 

 which has the form of a fish, appeared to move with 

 the least resistance; and soaked planks suffered a greater 

 resistance than those which were not soaked. 



6. Comparison of the Results of different Formulae and 

 Experiments. 



Dr Thomas Young has drawn up the following va- Compai 

 luable Table, containing a comparison of different for- of the n 

 mute with the experiments of Eytelwein, Bossut, and r ult nt f 

 those of the Society for the advancement of Naval m ^,, ^ 

 Architecture. In these formula, a is the angle ofexperi- 

 inclination, and R the resistance. meets. 



Formula A deduced by Dr Young, is R = cos. 2 a -j- 



T V tang. a. 

 Formula B deduced by Dr Young from theory is 



R= ^ + T ^tang. a +288 cos. 2 a :3604-a*. 

 Formula C deduced by Dr Young from experiments, 

 is R=cos. 2 a + .0000004217 a 5 - 18 in which the 

 last term is a little less than the millionth of the 

 cube of the angle of incidence expressed in de- 

 grees. 

 Eytelwein's formula is cos. 2 a -}- y^. versed sin. a. 



TABLE containing Dr Thomas Young's Comparison of different Formula! and Experiments. 



Oscillation 

 ei' fluids. 



We have purposely omitted giving any account of the 

 experiments of Hutton, Schober, and Colonel Beaufoy, 

 on the resistance of air, as they do not belong to the 

 present article. 



CHAP. VI. 



ON THE OSCILLATION OF FLUIDS, AND THE UNDULA- 

 TION OF WAVES. 



PHOP. I. 

 THE oscillations of a fluid in a syphon are isochro. 



nous, and are performed in the same time as those of a 

 pendulum, whose length is equal to half the length of 

 the oscillating columns. 



Let MNOP, Plate CCCXIX. Fig. 12. be a syphon, On the< 

 consisting of two vertical branches MN, OP, connected cillation 

 together by a horizontal branch NO, and having the " u ' Js - 

 same internal diameter throughout its whole length. If if,I?5 



t i -n T* * CCLA1 



water is poured into the syphon till it stands at AB in p,g. jjj. 

 one leg, it will stand at CD in the other, ABCD being a 

 horizontal line. Let a piston be now introduced at 1", 



