'6 NOTES OF A NATURALIST. 



the north-east trade wind, and my mind was some- 

 what exercised to account for the circumstance, said 

 to be of usual occurrence, that the breeze increases in 

 strength from sunrise during the day, and falls off, 

 though it does not die away, towards nightfall. It is 

 easy to understand the cause of this intermittence in 

 breezes on shore, whether near the sea-coast or in the 

 neighbourhood of mountain ranges, inasmuch as their 

 direction and strength are determined by the unequal 

 heating of the surface ; but the trade winds form a 

 main part of the general system of aerial circulation 

 over the surface of our planet, and, supposing the 

 phenomenon to be of a normal character, the explana- 

 tion is not quite simple. Regarding the trade wind 

 as a great current set up in the atmosphere, it is con- 

 ceivable that the heating and consequent expansion 

 which must occur as the sun acts upon it, tends to 

 increase the rate of flow at the bottom of the aerial 

 stream, while the cooling which ensues as the sun's 

 heat is withdrawn, has the contrary effect. 



On this and the next day or two my attention was 

 called to the frequent recurrence of masses of yellow 

 seaweed, sometimes in irregular patches, but more 

 frequently arranged in regular bands, two or three 

 yards in width, and extending in a straight line as far 

 as the eye could reach. We were here at no great 

 distance from the great sargassum fields of the 

 Northern Atlantic, but I was unable to satisfy myself 

 that the species seen from the steamer was that which 

 mainly forms the sargassum beds ; and, whatever it 

 might be, this arrangement in long straight strips 

 seemed deserving of further inquiry. More flying-fish 



