74 Mr. H. H. Howorth on 



of disturbance is to be measured not by the weight of the 

 whole polar column, but by the difference between the 

 pressure of the polar and equatorial columns, and no 

 more. It is, as Dr. Croll says, as if two scales of a balance 

 each hold a ton weight, and are equally balanced, and a 

 pound is added to one of them. The scale to which the 

 addition is made sinks down, not with the pressure of a ton,, 

 but of a pound only. 



When we measure, therefore, the result of Dr. Carpenter's, 

 hypothesis we shall find that the amount of pressure and 

 consequent displacement is the weight of the water which 

 has been added to the polar column to restore its equilibrium 

 with the equatorial one ; and this is clearly to be measured 

 by no other standard than the difference in density, if any,, 

 resulting from difference of temperature between the water 

 at the equator and the pole. 



It is this difference in density which we have seen reason 

 to question the existence of, which would, if anything, cause 

 the polar column to sink, and a corresponding amount of 

 water to flow over it. 



Ignoring the important element of saltness, as Dr. Car- 

 penter does, and accepting the conditions as he presents 

 them, it is not difficult to measure this and thus to see 

 whether the force generated would be sufficient to create an 

 ocean current. Sir John Herschell long ago showed that 

 the force would be a very slight one. Dr. Croll's more 

 recent calculation is that in order to create statical equili- 

 brium the water at the equator must be about 4 feet 6 inches 

 higher than that at the poles. This then is the amount of 

 inequality of level created by the action of the sun upon 

 the water of the ocean. Inasmuch as, according to Dr. 

 Carpenter, the first movement is caused by the column, of 

 water at the pole being not equal to, but heavier than, and 

 therefore overbalancing that at the equator, we must 

 reduce this amount considerably, for it is obvious that we. 



