OF TIDES. 



Captain Cook, who spent three summers as near as the ice would 

 permit his approach towards the south pole, found on December 

 14, 1772, and from that date to the beginning of January 1773, 

 in latitude from 55 to 64* south, a vast compact body of ice which 

 prevented his further progress. The thermometer varied from 30* 

 to 35. Being immersed 1 00 fathom deep for about 20 minutes, 

 it came up 34;. and on the 13th of January 1774, n a repetition 

 of this experiment, the open air being 36*, the surface of the sea 

 33^, the thermometer came up 32. They found water generally 

 freeze at 33 * " We certainly had no thaw, (says he,) the mer- 

 cury keeping usually below the freezing point. Being near an island 

 of ice (December 24, 1772) 5O feet high and 400 fathom in circuit, 

 I sent the master in the jolly boat to see if any water ran from it. 

 He soon returned with an account there was not one drop, or any 

 other appearances of thaw." And in the summer of 1774 7.5 

 his experience was nearly similar. On the 13th of February 1775, 

 the thermometer stood at 29. In his third voyage to the north- 

 west coast of America, on the 17th of August 1778 in lat. 

 70 44', they were stopped by a field of ice 10 or 12 feet high, as 

 compact as a wall ; " further north it appeared much higher ; here 

 and there we saw upon it pools of water ; we tried but found no 

 current. July 7, 1779, lat. 69; stopped by a large field of ice, 

 presenting a great extent of solid and compact surface not in the 

 smallest degree thawed : the thermometer stood at 31." 



" As far as our experience went, the sea is clearer of ice in Au- 

 gust than in July, and perhaps it may be still freer in a part of 

 September. We tried the currents, and found them never to ex. 

 ceed a mile an hour ; we found the month of July infinitely colder 

 than August ; the thermometer in July was once 2S n , and very 

 commonly 30 ^, whereas it was seldom as low as the freezing point 

 in August." 



'* I am of opinion (says Captain Cook) that the sun contributes 

 very little towards reducing these vast masses of ice; for, althougli 

 Ihat luminary is a considerable time above the horizon, it seldom 

 ghines out more than a 'few hours at a time, and often is not seen 

 for several da>s in succession. It is the wind, or rather the waves 

 raised by the wind, that reduces the bulk of these enormous masse.;, 

 by grinding one piece against another, and by undermining and 

 washing away those parts that lie exposed to the surge; and more 



