Dr. Carpenter on Mr. CrolPs "Crucial-Test" Argument. 403 



area. That in the latitude of the Mediterranean the thermal 

 condition of the North Pacific should be totally different, can 

 only (as it seems to me) be accounted for by its free communica- 

 tion with the Antarctic area ; for the Mediterranean is no more 

 warmed by wind-currents than the North Pacific, the Gibraltar 

 inflow (as my own observations demonstrate) being much colder 

 than either the surface-water of the Atlantic outside the Strait, 

 or the Mediterranean water within. 



If he could prove, as he asserts, that the Gravitation theory 

 makes water run up hill, this would doubtless be conclusive 

 against it. But his asserted proof rests on an assumption which 

 is a mere petitio principii — that of the equilibrium of the North 

 Atlantic and the Equatorial columns — without which assump- 

 tion no computation of their relative temperatures can possibly 

 make out the North Atlantic column to have a higher level 

 than the Equatorial. 



But further, even if their equilibrium were admitted, there is 

 a countervailing condition of which Mr. Croll does not seem to 

 have taken any account, viz. the inferior salinity of Equatorial 

 water, which will make a difference in the opposite direction of 

 about 1 foot in 1026, thus neutralizing Mr. CrolPs excess of 3J 

 feet in a column of only 600 fathoms depth. 



Again, Mr. CrolFs assertion that the Gravitation theory requires 

 a higher level for Equatorial water, rests upon the doctrine of the 

 " gradients " necessary to keep water in motion, which theory 

 and experience alike contradict. The researches of which Mr. 

 Froude gave an account at the Bristol Meeting of the British 

 Association, show that water is so nearly a " perfect fluid," that 

 its " viscosity " may be practically disregarded when the question 

 is one of the movement of water upon itself, not over solid sur- 

 faces. And they thus confirm the position I have all along 

 maintained, that a slow vertical circulation will be kept up 

 through the whole length of a basin filled with water that is 

 continuously subjected to surface-cold at one end and to surface- 

 heat at the other, without any appreciable difference of level be- 

 tween the two extremities. As an instance of the slight differ- 

 ence in sp. gr. which will suffice to maintain such a movement, 

 Mr. Eroude informed me that in an extensive examination of har- 

 bours, lochs, fiords, &c, he had found that a very small dilution of 

 their contents by fresh water is sufficient to produce an inward 

 underflow of sea-water,, tending to restore the disturbed equili- 

 brium. 



The doctrine of a vertical Thermal circulation was first put 

 forward by Lenz (well known to his contemporaries as a most 

 able physicist) nearly thirty years ago, as the only one which would 

 account for the phenomena of Deep-sea temperature ascertained 



2D2 



