which occasionally occur in England. 319 



" It is seen by the preceding memorandum, that in the pas- 

 sage from Plymouth to Madeira, the Iphigenia found the 

 temperature of the sea, between the parallels of 44|° and 33§°, 

 several degrees warmer than its usual temperature in the same 

 season; namely 3°'2 in 44^°, increasing to 6° in 39°, and 

 again diminishing to 4° in 33§° ; whilst at the same period, 

 the general temperature of the ocean in the adjoining parallels, 

 both to the northward and to the southward, even as far as 

 the Cape Verd Islands in 19f°, was colder by a degree and 

 upwards than the usual average. The evidence of many care- 

 ful observers at different seasons and in different years, whose 

 observations have been collected and compared by Major 

 Rennell, has satisfactorily shown, that the water of the Gulf- 

 stream, distinguished by the high temperature which it brings 

 from its origin in the Gulf of Mexico, is not usually found to 

 extend to the eastward of the Azores. Vessels navigating the 

 ocean between the Azores and the continent of Europe, find 

 at all seasons a temperature progressively increasing as they 

 approach the sun ; the absolute amount varies according to 

 the season, the maximum in summer being about 14° warmer 

 than the maximum in winter; but the progression in respect 

 to latitude is regular, and is nearly the same in winter as in 

 summer, being an increase of 3° of Fahr. for every 5° of lati- 

 tude. It is further observed, that the ordinary condition of 

 the temperature, in the part of the ocean under notice, is 

 little subject to disturbance, and that in any particular parallel 

 and season, the limits of variation in different years are very 

 small ; after westerly winds of much strength or continuance, 

 the sea in all the parallels is rather colder than the average 

 temperature, on account of the increased velocity communi- 

 cated to the general set of the waters of the north-eastern 

 Atlantic towards the south. To the heavy westerly gales 

 which had prevailed almost without intermission in the last 

 fortnight in November, and during the whole of December, 

 may therefore be attributed the colder temperatures observed 

 in the latitude of 47|°, and in those between 26° and 19^°. 



" If doubt could exist in regard to the higher temperatures 

 between 44^° and 33§° being a consequence of the extension 

 in that year of the Gulf-stream in the direction of its general 

 course, it might be removed by a circumstance well-deserving 

 of notice, namely, that the greatest excess above the natural 

 temperature of the ocean was found in or about the latitude 

 of 39°, being the parallel where the middle of the stream, in- 

 dicated by the warmest water, would arrive, by continuing to 

 flow to the eastward of the Azores, in the prolongation of the 

 great circle in which it is known to reach the mid- Atlantic. 



