364 Professor Faraday [May 3, 



four inches in diameter. The image so magnified together with posi- 

 tion wires are depicted on the collodion plate placed in the telescope. 

 In taking ordinary sun pictures, or pictures of the partial phases of the 

 eclipse, the light is allowed to act on the sensitive plate by the passage 

 of a narrow slit in a brass plate drawn with great rapidity across the 

 secondary magnifying lens. By this contrivance, the sun's image is 

 allowed to act for a very small fraction of a second of time. Thirty- 

 one pictures of the various partial phases of the eclipse were obtained 

 in this way by Mr. De la Rue and his assistants. Several of the most 

 interesting were projected on to the screen by means of the electric lamp. 

 The two totality pictures were, however, obtained in another way ; the 

 brass plate with the slit was drawn aside, and the picture of the pro- 

 tuberances allowed to fall for a whole minute on the collodion plate. 

 The first picture was procured exactly from the commencement of the 

 totality and during the minute precisely succeeding it. The second 

 picture from about a minute preceding the reappearance of the sun 

 until just before he reappeared. 



These pictures were shown on the screen by means of the electric 

 lamp, and it was seen that the luminous prominences extended for a 

 long distance beyond the moon's dark limb. In the first picture, some 

 prominences were completely detached, and were at some considerable 

 distance from the moon's limb ; these, in the second picture, were reached 

 by the moon, which during the interval had been travelling across the 

 sun's disc. Fresh prominences had come into view in the second pic- 

 ture on the western limb, while some of the prominences on the eastern 

 limb had been shut off by the moon's motion. 



The speaker then referred to diagrams, which had been enlarged 

 from actual photographs, etched upon glass by hydrofluoric acid, and 

 graduated in accordance with the data furnished by the images of 

 position wires on the photographs. These diagrams showed that a 

 luminous prominence situated at a right angle to the path of the 

 moon's motion across the solar disc had hung back in reference to the 

 moon's centre an angular distance of about 5^°, while prominences 

 situated in the direction of the moon's path had not shifted angularly, 

 but were covered and uncovered to an extent of about 93" during the 

 period of totality. Such results were in accordance with the hypo- 

 thesis that the prominences belong to the sun, and opposed to the 

 theory that they are subjective phenomena produced by the deflection 

 of the sun's light. 



In order to render evident the relative positions of the whole of the 

 protuberances visible during the eclipse, attention was drawn to a 

 diagram enlarged from an etched photograph of the sun, on which were 

 etched also the protuberances visible in the first and second totality 

 — photographs which coincided exactly when superposed in respect of 

 those parts visible in both. It was seen on the diagram, that in con- 

 sequence of Rivabellosa not being exactly in the centre of the shadow 

 path, the moon's centre was depressed below the sun's centre, and thus 

 at the nearest approach of the two centres they were distant about 14". 



