LUMINOUS SHOWERS. 153 



Professor Ehrenberg knows many species af infusoria pecul- 

 iar to Africa, he finds none of them in the dust which I sent 

 him; on the other hand, he finds in it two species which 

 hitherto he knows as living only in South America. The 

 dust falls in such quantities as to dirty every thing on board, 

 and to hurt people's eyes; vessels even have run ashore, 

 owing to the obscurity of the atmosphere. It has often 

 fallen on ships when more than a thousand miles from the 

 coast of Africa, and at points sixteen hundred miles distant 

 in a north and south direction. In some dust which was 

 collected on a vessel three hundred miles from the land, I 

 found particles of stone, above the thousandth of an inch 

 square, mixed with finer matter. After this fact, one need 

 not be surprised at the diffusion of the far lighter and smaller 

 sporules of cryptogamic plants." 



The extent to which dust and ashes can be taken up and 

 held by air currents is shown in volcanoes. In 1810 the 

 ashes from a volcano at St. Vincent were wafted to Barba- 

 does, nearly a hundred miles ; and in 1835 the material 

 thrown from a volcano in Guatamala to Jamaica, eight hun- 

 dred miles. As intimated, these showers are not all inor- 

 ganic, but are often living or fossil animals or plants that 

 are floating about. Such are the reddish or gray showers 

 that are frequently met with off the African coast, and when 

 in the snow they are called "blood-rains." The one in 

 1755, near Lago Maggiore, covered over two hundred square 

 leagues, causing a panic among the inhabitants. For a dis- 

 tance of nine feet below the surface, the snow was blood 

 red, the atmosphere appeared red and fiery, while at sunrise 

 and sunset a rosy hue pervaded every thing. When tliis 

 shower fell and there was no snow, the earthy deposit accu- 



