56 LIGHT SCIENCE FOR LEISURE HOURS. 



far as the comparison made between these two sets of 

 photographs was concerned, it appeared as though the 

 solar prominences were fixed objects ; and some went 

 so far as to conclude definitely that they are real solar 

 mountains. 



It was not until the great eclipse of August 1868 

 that the real nature of the coloured prominences was 

 ascertained. This eclipse was distinguished from all 

 that had ever been observed before by the duration of 

 totality. For more than six minutes the disc of the 

 sun was completely hidden from view. It need hardly 

 be added that the shadow on the earth's surface was 

 exceptionally wide ; so that near the middle of totality 

 at any station along the central line the observer was 

 in the centre of a nearly circular region of the earth 

 more than 150 miles in diameter, and to which not a 

 ray of direct sunlight penetrated. All the features of 

 the eclipse were thus observed under singularly favour- 

 able circumstances. 



In the first place, it was possible to obtain more 

 photographs than on any former occasion. Lieutenant- 

 Colonel Tennant, using a fine 9-inch reflector made by 

 Mr. J. Browning, F.R.A.S., obtained no less than six 

 photographs, coloured pictures of which lie before me 

 as I write. The first shows a glare of light on the 

 left, where the moon had not as yet covered the last 

 fine line of the sun's disc. Yet we see through the 

 glare the figures of the prominences on that side 

 showing ' as through a glass darkly ' and amongst 

 them that mighty horn-prominence whose spiral whorls 



