264 Mr J. Croll on the Physical Cause of Ocean-currents. 



considerable resistance to motion. Now, if the resistance offered 

 by water to motion exceeds the pressure of - ST) V of a grain per 

 pound, gravity will be unable to cause the water to flow down 

 the incline under consideration ; for were it to do so, the work 

 of the resistances would exceed the work of gravity — a thing 

 impossible. If the resistances of the water to motion equalled 

 5^-q of a grain per pound, the entire 9 foot-pounds of energy 

 would be expended in carrying the pound of water from the 

 equator to the pole, and no energy would remain to cause 

 the water to descend to the bottom of the ocean, to return to the 

 equator as an under current, and then to ascend to the surface. If 

 we assume, what certainly must be the case, that the total amount 

 of resistance offered to the motion of the water in the under- 

 current and in the two vertical currents equals the resistance 

 offered in the surface -current, then the force of the resistance to 

 the pound of water, if motion is to take place, must be under 

 Tooo °f a g ram - For as we have only 9 foot-pounds of energy 

 for the entire circuit, 4^ foot-pounds would be spent on the 

 surface-current, and the other 4-| foot-pounds would go to pro- 

 duce the under and two vertical currents. But if the resistances 

 exceeded xoVo" °f a g ram on tce pound of water, the work of 

 the resistances in the entire circuit would exceed the work of 

 gravity, and consequently no motion would be possible. M. 

 Dubuat, as has already been stated*, found that water remains 

 motionless on an incline of 1 in 1,000,000 ; but such an incli- 

 nation gives for the force of gravity j\^ of a grain. This shows 

 that the resistance to the motion of the water amounts to at 

 least yjg of a grain. But before circulation can take place, ac- 

 cording to Dr. Carpenter's theory, the resistance of the water 

 would require to be only one seventh of that amount, viz. joVo 

 of a grain. We are therefore led to the conclusion that it is ab- 

 solutely impossible that difference of specific gravity can produce 

 even motion of the waters of the ocean, far less such a circula- 

 tion as that assumed by Lieut. Maury and Dr. Carpenter. 



I have not been able to find any direct determinations as to 

 the work of the resistances in the flow of water ; but the above 

 show indirectly that it must far exceed the work of gravity. 

 Canon Moseley has lately been investigating the question of 

 the resistance of fluids by means of his new method, which he 

 had applied with such remarkable success to glacier-motion f. 

 By this methed he has been able to determine the amount of 

 the internal work of resistance of the films of water to the flow- 

 ing of each film over the surface of the next in succession ; and 

 there is little doubt but he will be able to settle the question 



* Phil. Mag. October 1870, p. 251. 



f Phil. Mag. for September 1871, p. 184. 



