60 MR RUSSELL'S RESEARCHES IN HYDRODYNAMICS. 



by the untoward circumstance of the disturlance which is caused by the protru- 

 sion of a solid into the space occupied by the fluid. The particles which are thus 

 displaced are thrown aside by the anterior part of the body, and then collapse 

 upon other parts of it ; or they are thrown forward before the body, which is after- 

 wards protruded on them a second time ; or they are thrown up in heaps in cer- 

 tain forms of equilibrium, and the accumulations and irregularities of pressure 

 which are thus occasioned give rise to currents of the fluid and mutual collisions 

 amongst divided masses of it, and surges and other phenomena, all of which en- 

 tering at once as elements of the resistance into the production of the resulting 

 phenomena, do so modify them, as to give results that are totally inconsis- 

 tent with theory, and are apparently at variance with each other. That theory, 

 therefore, which will venture to assign the measure of the resistance of a fluid to 

 a sohd, upon the supposition that the surface of the fluid remains horizontal, and 

 that the anterior part of the solid finds the sm-face of the liquid a level plane, will 

 proceed upon imperfect data. 



The only one of these disturbing causes which has hitherto been investigated 

 in theories of hydrodynamics, is the lateral current proceeding from the stem to- 

 wards the stern of the moving body. 



The elements which I have added to those previously investigated are the 

 Anterior, Posterior, and Central Waves. 



I was first led to investigate the disturbances produced by the entrance of a 

 floating solid into a quiescent fluid, by encountering a series of anomalous irregu- 

 larities in my attempts to measure the immersion and resistance of the floating 

 body at different velocities. There were certain velocities at which the body ap- 

 peared to be almost buried in the water, and was so much impeded, that any force 

 employed to accelerate the velocity of the body seemed only to accumulate resist- 

 ance upon it, while at other velocities greater or less than these, the body would 

 suddenly change its position, and instantly emerge out of the trough of the fluid 

 to a considerable height above its statical elevation. But what happened in one 

 portion of fluid did not occur in a different portion of the same fluid even at the 

 same velocit3^ The resistance would sometimes exceed the third power, and again 

 in another portion of fluid fall below the first power, for the very same velocity. 

 These were disruptions of the law of continuity which the gradual law of an emer- 

 sion as a function of velocity and gravity alone could not solve. I therefore entered 

 upon a series of inquiries, directed solely to the subject of discovering and determin- 

 ing the unknown constituents of the disturbance of the equilibrium of the fluid occa- 

 sioned by the presence of the floating body. The results of my inquiries I am now 

 to state as briefly as clearness will allow, premising, at the same time, that the 

 facts which presented themselves appeared at first to myself as extraordinary as 

 the}^ may now probably seem to those who may learn them for the first time ; but 



