90 EXPEDITION TO JAPAN. 



The hypothesis of some is, that in passing over the deserts and lands of Africa the 

 "Harmattan" takes up an immense quantity of sand and dust, sufficient to form a floating 

 mass, producing an atmosphere so hazy as frequently to obscure the sun, and prevent a sight of 

 the land at the distance of five miles only. There is no doubt of the wind, the dust, and the 

 hazy atmosphere, and possibly the latter may be occasioned entirely by the dust. At the season 

 of the "Harmattan" this peculiar atmosphere may always be seen at the Cape de Verd islands, 

 four hundred miles from the continent, and is constantly falling in quantities sufficient to cover 

 the sails, rigging, and deck of a ship. It is also said to have been met with seven hundred 

 miles further westward. 



Kecent investigations, however, certainly create some doubt as to the source whence the 

 dust is derived. It was natural enough, as it was foimd on the coast of Africa, to refer its origin 

 to the nearest known desert land; but the microscope, in the hands of Ehrenberg, would seem 

 to intimate the possibility of a more distant origin. This dust, from the Cape de Verds, is 

 found, upon examination, to consist of infusoria and organisms, the habitat of which is not 

 Africa, but Smith America, and in the southeast trade wind region of that country. It is, 

 therefore, possible that the southeast trades may have brought the dust, great as is the distance, 

 from South America. But if such be the fact, it must be confessed that there are agencies in 

 the philosophy of the winds, producing atmospheric phenomena, which are not yet sufficiently 

 understood by us to justify positive assertion. A greater accumulation of facts is wanted. 

 That stated by Ehrenberg is very important, and quite sufficient to create doubt of the correct- 

 ness of the ordinary hypothesis. 



Until the 30th of December the northeast trades continued, the ship having then reached 

 6° 8' north latitude, and 16° 34' west longitude, when, in a squall from the eastward, the wind 

 changed to the southward, and so continued, though somewhat variable, until January 2, 1853, 

 in latitude 1° 44' north, and longitude 11° 37' west, when the southeast trade was met, bringing 

 with it a swell, which retarded the ship's progress considerably. Before this, however, on the 

 29th of December, as the northeast trades had become light and unsteady, with occasional 

 calms, the floats were replaced on the wheels, and the ship was put under steam, using the two 

 after boilers only. With light winds and a smooth sea, these proved sufficient to make a 

 progress of seven knots an hour ; but when the southeast trades fairly set in, accompanied as 

 they were by a head sea, the speed was diminished to four and a half or five knots. The use 

 of two additional boilers, however, soon brought the ship up to seven, at a daily consumption 

 of twenty-six tons of coal. 



It had been the purpose of the Commodore, on leaving Madeira, to make the entire run to the 

 Cape of Good Hope without stopping ; as it was supposed that with a proper use of the sails, 

 and the supply of coal on board, this might readily be done ; but the northeast trades having 

 ceased at a point much further north than usual at this season, and the southeast winds having 

 also set in at a correspondingly early period, he ordered the ship so to be steered as that she 

 might touch at St. Helena, should it be deemed desirable so to do, as a measure of prudence, to 

 procure an additional supply of coal. 



In the observations made upon the currents since leaving Norfolk, the Commodore was of 

 opinion that such as he encountered were caused merely by the winds acting on the surface of 

 the ocean ; and as a general rule, though not perhaps universally true, it may be remarked 

 that the current will be found setting in the direction of the prevailing winds; at least 



