56 MR RUSSELL'S RESEARCHES IN HYDRODYNAMICS. 



contrary, as will be apparent in the sequel, that great and marked facilitation of 

 the motion is observed when the line of effect of the moving force has a down- 

 ward, instead of an upward, direction ; and that any elevation of the prow or an- 

 terior part of a vessel, instead of facilitating its motion, increases the resistance 

 to it. 



To determine the real condition of the immersion of the floating body at 

 various velocities, and trace the phenomena to some kno'vvn mechanical principle, 

 was the object of the first series of my experiments in 1834. For this purpose 

 there was constructed an experimental skiff, a very light vessel of a very small 

 draft of water, and furnished with apparatus for determining resistance and im- 

 mersion. The skiff and its apparatus are described and delineated in that part 

 of this paper which contains the details of the experiments of 1834. Chronome- 

 ters, d3Tiamometers, and two modifications of Pitot's tube were observed. Twelve 

 openings in the bottom of the vessel allowed the water to rise in glass-tubes care- 

 fully graduated, to the level of the fluid without, and furnished measures of the 

 statical and dynamical immersion of the floating body. The vessel thus furnish- 

 ed, was made the subject of careful experiment at velocities of from 3 to 20 miles 

 an hour. 



These experiments give a decided and consistent result. It was found that 

 in every case the statical immersion of the floating body was less than its dyna- 

 mical immersion. The following are taken from the experiments of 1834, given 

 in Part IT. The statical immersion being 2.7 inches, the dynamical immersions 

 observed at given velocities in miles an hour were as follows — 



Velocity, 0. , 3.016, 4.00, 5.165, 6.431, 7.253, 8.11, 9.164, 10.237, 20. -|- 

 Immer. 2.7, 2.6 , 2.5 ,2.2 ,1.9 , 1.8 , 2.2 , 2.3 , 2.0 , 1.5 



After having determined the existence of a dynamical emersion, I endea- 

 voured to discover the law of connection between the diminished immersion and 

 the velocity of the motion. A singular change in the immersion at the velocity 

 8.11, and those immediately following it, gave me much trouble in my attempts 

 to do this. I at first imagined the experiments might have been erroneous, but 

 obtained the same results on each repetition. It afterwards turned out that these 

 very anomalies shewed the continuity of the law ; for it will soon be apparent in 

 following out the subject, that at that very velocity of 8.11, the fluid undergoes 

 a very extraordinary change in its form, which increases the immersion at the 

 middle of the floating body when these immersions had been observed, and dimi- 

 nishes it at other parts of the body. Leaving, therefore, indications 8.11, and 

 those which succeed it, to have the reductions made upon them, which subse- 

 quent investigations render necessary, and taking those below that point, and far 

 above it, we may now proceed to examine whether any known principle will 

 lead us to assign a law accordant with these phenomena. 



