426 Dr. J. R. Mayer on Celestial Dynamics. 



We have plenty of observations which prove that the earth 

 suffers a great loss of heat through the waters of the ocean. 

 Many investigations have demonstrated the existence of a large 

 expanse of sea, much visited by whalers, situated between Ice- 

 land, Greenland, Norway, and Spitzbergen, and extending from 

 lat. 76° to 80° N., and from long. 15° E. to 15° W. of Green- 

 wich, where the temperature was observed to be higher in the 

 deeper water than near the surface — an experience which neither 

 accords with the general rule, nor agrees with the laws of hy- 

 drostatics. Franklin observed, in lat. 77° N. and long. 12° E., 

 that the temperature of the sea near the surface was — J°, and 

 at a depth of 700 fathoms +6°. Fisher, in lat. 80° N. and 

 long. 11° E., noticed that the surface-water had a temperature 

 of 0°, whilst at a depth of 140 fathoms it stood at + 8°. 



As sea-water, unlike pure water, does not possess a point of 

 greatest density at some distance above the freezing-point, and 

 as the water in lat. 80° N. is found at some depth to be warmer 

 than water at the same depth 10° southward, we can only ex- 

 plain this remarkable phenomenon of an increase of temperature 

 with an increase of depth by the existence of a source of heat 

 at the bottom of the sea. The heat, however, which is required 

 to warm the water at the bottom of an expanse of ocean more 

 than 1000 square miles in extent to a sensible degree, must 

 amount, according to the lowest estimate, to some cubic miles 

 of heat a day. 



The same phenomenon has been observed in other parts of the 

 world, such as the west coast of Australia, the Adriatic, the 

 Lago Maggiore, &c. Especial mention should here be made of 

 an observation by Horner, according to whom the lead, when 

 hauled up from a depth varying from 80 to 100 fathoms in the 

 mighty Gulf-stream off the coast of America, used to be hotter 

 than boiling water. 



The facts above mentioned, and some others which might be 

 added, clearly show that the loss of heat suffered by our globe 

 during the last 2500 years is far too great to have been without 

 sensible effect on the velocity of the earth's rotation. The 

 reason why, in spite of this accelerating cause, the length of a 

 day has nevertheless remained constant since the most ancient 

 times, must be attributed to an opposite retarding action. 

 This consists in the attraction of the sun and moon on the 

 liquid parts of the earth's surface, as explained in the last 

 chapter. 



According to the calculations of the last chapter, the retard- 

 ing pressure of the tides against the earth's rotation would 

 cause, during the lapse of 2500 years, a sidereal day to be 

 lengthened to the extent of t« th of a second ; as the length of 



