362 NOTES OF A NATURALIST. 



what seamen describe as a fresh breeze, but it sufficed 

 to cause at times considerable disturbance of the 

 surface ; and on the afternoon of the 6th we shipped 

 some heavy seas, so that it was foUnd expedient to 

 slacken speed for a time. 



I have alluded in a former page to the ordinary- 

 observation that in the track of the trade winds the 

 breeze usually falls off about sunset. It is more 

 difficult to account for the opposite phenomenon, 

 which we experienced on three successive evenings 

 from the 7th to the 9th of August, when the force of 

 the wind increased in a marked degree after nightfall. 



I was also struck by the fact that the temperature 

 of the air throughout the voyage from St. Vincent to 

 the mouth of the Tagus seemed to be unaffected 

 either by the varying force of the wind or by^the fall 

 in surface-temperature of the sea, to which I have 

 above referred. On board ship in clear weather it is 

 very difficult to ascertain the true shade-temperature 

 when the sun is much above the horizon, but the 

 observations made at sunrise and after nightfall from 

 the evening of the 5th to the morning of the nth 

 varied very slightly, the utmost range being from 

 77-5° to 73°. 



Some points in the Canary Islands are often visible 

 in the voyage from Brazil to Europe, especially the 

 lofty peak of Palma ; but we passed this part of the 

 course at night, and nothing was seen. As we drew 

 near to Europe, the wind, through keeping the sam 

 direction, gradually fell off to a gentle breeze, and the 

 surface of the water became glassy smooth, heaving 

 gently in long undulations. The relative effect of 



