182 ANNUAL OF SCIENTIFIC DISCOVERY. 



taken with his " heliautograph," which consists of a camera and in- 

 stantaneous slide, by Dallmeyer, attached to a refractor of 2f inches ' 

 aperture, by Dollond; the principle being the same as that of the 

 instrument made at the suggestion of Sir J. Herschel for the Kew 

 Observatory. Three of these autographs were taken on the 23d day 

 of August, 1862, and two of them had the edge of the sun in the 

 centre of the photographic plate, showing that the diminution of light 

 towards the edges of the disc is a real phenomenon, and not wholly 

 due to the camera. In two of the 4th of August, where a great 

 spot (20,000 miles in diameter) appears on the edge, a very distinct 

 notch is seen, and the sun appears to give strong evidence that the 

 spots are cavities ; but eye observations and measurements by the 

 Rev. F. Hewlett, and others, tend to show that this evidence is not 

 conclusive, for there was still a remaining portion of photosphere be- 

 tween the spot and the edge. The phenomena shown in these auto- 

 graphs appear to confirm the views of Sir J. Herschel, that the two 

 parallel regions of the sun where the spots appear are like the tropi- 

 cal regions of the earth, where tornadoes and cyclones occur, and 

 those of Wilson in the last century. The faculce seem to show that 

 the tropical regions of the sun are highly agitated, and that immense 

 waves of luminous matter are thrown up, between which appear the 

 dark cavities of the spots, whose sloping sides are seen in the penum- 

 brae, as explained by Wilson and others. 



By means of photographs of the sun, taken every fine day at the 

 Kew Observatory, England, we are now obtaining a continuous his- 

 tory of the changes in the spots and faculas on its face, more accurate 

 and more instructive than could be procured by any verbal descrip- 

 tion or ordinary drawing. By this means, questions relating to the 

 periodicity of these changes, and their connection with terrestrial 

 magnetism, will be solved, and likewise those concerning the move- 

 ments of the supposed ring of asteroids in the region of Mercury. 



Micro-Photographs. The Abbe Moigno gives a most enthusiastic 

 account of the new method of preparing and exhibiting micro-photo- 

 graphs invented by M. Dagron. After describing a process by which 

 a series of the minute sun pictures are taken in rapid succession, he 

 proceeds to inform us that a number of cylinders of common or flint 

 glass are prepared in advance, about five or six millimetres long and 

 two thick. One extremity of these cylinders is spherically rounded 

 in a hollow, to transform it into a magnifying lens ; while to the other 

 extremity of the cylinder a micro-photograph is fixed with Canada 

 balsam, and the edges ground by an optical tool to efface the marks 

 of the union. This is the photo-micrographic cylinder. 



Photo-zincography. From the first introduction of daguerreotypes 

 to the present time, there have constantly been attempts to etch the 

 photographic image or to transfer the solar picture to stone. The 

 photo-galvanographic process will be familiar to many, and Mr. Fox 

 Talbot's engravings have been widely displayed. From time to time, 

 too, photo-lithography has promised great results ; but both in this 

 country and in Europe difficulties have arisen in practice which have 

 prevented success. Nearly all of these processes have been founded 

 on the use of the bichromate of potash in contact with gelatine or 

 some analogous organic body. 



