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ME. WAEEEN DE LA ETJE ON THE 
conviction that they are far more generally distributed on the solar disk, and of propor- 
tions greatly exceeding any which the spots ever attain to. 
Since the prominences would appear to be scattered so widely over the sun’s surface, 
the question has arisen whether it would be possible to render these wonderful append- 
ages apparent at other periods than those of total eclipses of the sun. For the pm’pose 
of solving this problem, Mr. James Nasmyth devised an apparatus which, in part, con- 
sisted of a cylindrical box, blackened inside, having in one end an aperture of such dimen- 
sions that it exactly permitted of the passage of the sun’s image when projected by a 
telescope, whilst the surface surrounding the aperture was sufficiently large to receive 
the images of all objects situated beyond the solar periphery. 
The Astronomer Eoyal also has made experiments vrith the same view, using, in part, 
the Nasmyth apparatus ; but the existence of the luminous prominences could not be 
detected by its means, in all probability on account of the great amount of illumination 
of that part of our atmosphere which is in apparent contiguity with the sun. On the 
occasion of Professor Piazzi Smyth’s experimental visit to the Peak of Teneriffe he took 
out with him this apparatus, because it was thought that the more attenuated stratum 
of atmosphere at that elevation would interfere less with the success of the experiment. 
Only negative results were, however, obtained, and the problem remains to be solved. 
Is it probable that photography may lead to a solution of the difficulty! I am 
inclined to think that it may possibly do so. It would, however, be quite futile to 
attempt to delineate the luminous prominences, when beyond the sun’s periphery, by 
means of photography, after the experience afforded by the experiments before cited ; 
for most unquestionably they would not produce an image so intense as that of om.’ own 
atmosphere in apparent contiguity with the sun’s disk and illuminated by his rays. My 
hope is that their forms may be depicted on the brighter solar disk itself, and their 
existence rendered evident by means of the stereoscope, which has akeady enabled me 
to make out the real nature of the radiating lines on the lunar surface. 
During the year 1861, by means of my 13-inch equatorial reflector, 1 succeeded in 
procuring photographs of the sun’s surface, on a scale of 3 feet for the sun’s diameter. 
These colossal photographs were obtained by enlarging the focal image by means of a 
secondary magnifier, constructed especially to ensure a flat field and the coincidence of 
the visual and chemical foci. They show, in a remarkably striking mamier, the mottling 
of the sun’s photosphere, which appears to be entirely composed of an undulating mass 
of waves, like the surface of the sea agitated by wind. 
Two pictures of the same sun-spot, taken at an interval sufficiently great to admit of 
the sun’s rotation causing the necessary angular shift of its position, evidently possess 
the stereoscopic relation. By placing them in the stereoscope in such a way that the 
positions of the two pictures, relatively to each other, shall be reversed, that last taken 
being placed on the left, that first taken to the right (supposing the image to be erect), 
I have obtained a stereoscopic picture of a sun-spot, and some surrounding faculse, 
which represented the various parts of the picture in their true relative positions in 
