144 ANNUAL OF SCIENTIFIC DISCOVERY. 



turbance in our own atmosphere." Mr. Dawes states his conviction o 

 the superiority of large apertures with high powers in viewing the sun. 

 which this reduction of the field makes easy. The facula3, too, ar< 

 seen far better with large apertures, especially when the power is no 

 proportionally high. " These are best seen near the east and" wes: 

 edges of the sun's disc, where they give the impression of narrov. 

 ridges, whose sides are there presented to view. They usually lit- 

 nearly in the direction of a circle of latitude on the sun's surface, and 

 are rarely high enough to be seen as actual projections from his limb. 

 On one occasion, however, the 22d of January last, I had an oppor- 

 tunity of observing a satisfactory confirmation of the idea that they 

 are ridges, or heapings up of the luminous matter ; and as the requisite 

 circumstances are extremely rare, I will advert more particularly to 

 the observation. A large bright streak, or facula, was observed to run, 

 as usual, nearly parallel to the sun's edge for some distance, and very 

 near it ; and then to turn rather abruptly towards the edge and pass 

 . over it. The limb was at times very well defined ; and when it was 

 most sharp and steady, the bright streak was seen to project slightly 

 beyond the smooth outline of the limb, in the manner of a mountain 

 ridge nearly parallel to the sun's equator." This eye-piece was 

 applied to Mr. LasselFs 20 foot reflector last September, and the sun 

 was examined with the whole of the 24 inch mirror. The eye-piece 

 did not become more than sensibly warm after two hours' exposure to 

 a brio-ht sun. Mr. Dawes points out the utility of this contrivance in 

 examining the surface of the moon, in observing occultations of small 

 stars, and the eclipses of Jupiter's satellites, and in observing or 

 detecting the faint satellites of planets. By such means, too, Venus 

 and Mercury may be more pleasantly observed when near the sun ; 

 and, as the author remarks, " to the practised observer such applica- 

 tions will readily occur," and need not be here insisted on. 



ON THE FORM OF IMAGES PRODUCED BY LENSES AND MIRRORS 



OF DIFFERENT SIZES. 



A PAPER on the above subject was read before the British Associa^ 

 tion by Sir David Brewster, the object of which was to show, that the 

 photographic portraits taken with cameras with large object-glasses or 

 large mirrors must necessarily be distorted and hideous, as in fact it is 

 notorious they are ; and that hence all persons engaged in this ne\\ 

 and most important art should receive with gratitude any scientifi 

 discovery which promised to correct so serious a defect- -which b) 

 some has been attributed to the imperfection of the lenses employed, 

 by others to the unsteadiness of the sitter who is having his portrai; 

 taken, --by others, again, to the constraint of features and limb unde 

 which he submits to the operation ; but it is by all admitted and 

 deplored. If we consider that the pupil of the* human eye is onh 

 about 2-10ths of an inch in diameter, it is obvious that the imao-e*. 

 formed by the eye of those solid objects placed in front of it, and by 

 which we are accustomed to see them, to judge of them, and to recpg. 



