CELESTIAL PHOTOGRAPHY.] TJNDULATORY FORCES. LI GHT PHOTOGRAPH Y. 



1C5 



peculiar appearances which are presented during an 

 eclipse of the sun. have afforded matter of deep discus- 

 sion on the part of astronomers. Of these, tht beads, red 

 flames, itc. , which are frequently seen in an annular or 

 total eclipse, are the most prominent. The intense ex- 

 citement which naturally affects the coolest observer 

 when phenomena of the deepest interest, and lasting 

 but a few seconds of time, take place, is enough to 

 unfit any one for taking accurate observations. Besides 

 this, the power and peculiarities of vision of each person 

 so engaged, vary to so great an extent, as to give an 

 entirely different complexion to the observations taken. 

 Photography here, therefore, steps in. The inanimate 

 paper is subject to no emotion, or disturbing cause, and 

 it affords a ready and efficient means of registering an 

 observation, which cannot possibly be otherwise than 

 accurate. 



For the purpose of obtaining varied and positive 

 results, some of the leading philosophers of our time 

 betook themselves to various places over which the 

 shadow of the moon would pass. They were abun- 

 dantly provided with instruments for ordinary and 

 photographic observation ; and when possible, the 

 duties of observing were divided amongst a number 

 of persons, so that each might make one phenomenon 

 his special duty to attend to. We must confine ourselves 

 entirely to the photographic results ; and are indebted 

 for such to the Photographic News Almanac, from which 

 the following extracts have been made : 



"M. Foucault studied the corona, both optically and 

 photographically. Immediately after the disappearance 

 of the last solar ray of direct light, a prepared plate was 

 exposed ten seconds ; then a second plate was exposed 

 twenty seconds; and lastly, a third plate was exposed 

 during sixty seconds : they were developed by sulphate 

 of iron, and fixed with cyanide of potassium, with the 

 object of obtaining direct positives. Owing to a vibra- 

 tion accidentally given to the apparatus, four images 

 were impressed on the first sensitive plate, in a very 

 short space of time ; three at least in less than a 

 quarter of a second each : these possessed a peculiar 

 interest and value ; they did not give a complete picture 

 of the aureola, but only of a circumference of the circle 

 surrounding the obscure disc of the moon. On the 

 side where the interior contact took place, the circular 

 contour presented greater intensity, which confirmed 

 the impression entertained by M. Leverrier. Irregu- 

 larities, similarly situated, on these three images were re- 

 marked, which appeared to be an exaggerated represen- 

 tation of the lunar contour. When the proofs were 

 placed in the actual position of the planets, it was seen, 

 that among the indentations, two were principal and 

 contiguous, situated at the inferior and eastern extre- 

 mity of a diameter inclined at forty-five degrees. The 

 three other proofs gave an extension to the aureola, 

 which increased with the duration of the exposure. The 

 aureola diminished in proportion as it receded from the 

 planet, and its line of demarcation became lost in the 

 tint of the ground which represented the sky. In the 

 proof exposed sixty seconds, the aureola extended sen- 

 sibly to a distance equal to thrice the radius of the 

 central disc. But, in certain particular directions, the 

 aureola exhibited positive and negative variations in its 

 intensity, producing the representation of a glory. One 

 of them, better defined than the other, was prolonged, 

 in all the proofs, beyond the rest of the aureola, and 

 seemed to emanate exactly from the point occupied by 

 the indentation on the edge of the moon, already de- 

 scribed. 



" Such are the results of an experiment undertaken 

 solely to ascertain the photogenic activity of the aureola 

 on wet collodion. The harmony prevailing among tho 

 six proofs, supply positive elements for the discussion 

 of the nature of the aureola." 



The Astronomer Royal, Dr. Airy, proceeded to Spain ; 

 and the following contains the substance of a paper read 

 by him Insfore the British Association, at the meeting 

 held in Manchester, in ^eptomber, 18i>l. 



In the early part of Jus discourse, Dr. Airy gave a 



general account of the cause and phenomena of eclipses ; 

 entering into a great variety of astronomical data, which 

 it would be foreign to our purpose to repeat. Having 

 disposed of the general nature of eclipses, he called at- 

 tention to some peculiar appearances, termed " Baily's 

 Beads" a number of bright spots, which have been no- 

 ticed on the edge of the sun just before an eclipse became 

 total In 1842, red flames were noticed as protuberances 

 from the edge of the sun ; but the surprise and unpre- 

 pared state of the spectators, unfitted them to make 

 accurate observations or detailed reports. In 1850, 

 during a solar eclipse, similar, and additional, pheno- 

 mena were noticed ; and due preparation having been 

 made to observe the same in 1851, several philosophers, 

 including Dr. Airy, proceeded to Sweden, and other 

 places, for the purpose of making a fresh series of obser- 

 vations. A variety of interesting results were obtained ; 

 but still, the uncertainty of human power, and the mental 

 excitement under which all the observers suffered, in- 

 validated any conclusions at which they arrived, and 

 still left much to be desired in the way of truthful 

 result. 



Accordingly, in 1860, a large party of astronomers, 

 and others, proceeded from this country to Spain, well 

 provided with apparatus of all kinds, and also with a 

 complete set of instruments, by means of which the 

 photographic art was put into full operation; and the 

 entire proceedings were attended with the greatest suc- 

 cess: Similar arrangements of clockwork, to which we 

 have already alluded, were employed, and an accuracy 

 of result was obtained which left scarce anything to be 

 desired. 



Amongst the most successful of the operations were 

 those by Mr. De la Rue ; which he conducted by means 

 of apparatus he had fitted specially for the purpose. The 

 annexed engraving represents a photograph of the eclipse 

 at its totality, and the red flames issuing from the outer 

 edge of the sun. 



Fig. 160. 



The photographs thus taken were subsequently com- 

 pared with those effected by other operators, and their 

 exact similarity was so great, as to prove the extreme 

 value of photography in its application to astronomical 

 observations. Indeed, many occurrences unperceived by 

 the observer were thus registered, and additional light 

 was thrown on a variety of previously obscure pheno- 

 mena. 



CONCLUDING REMARKS ON PHOTOGRAPHY. 



IN the preceding pages, we have endeavoured to present 

 the reader with a rt-sume of most of the photographic 

 processes in use at the present time, together with others 

 which have been superseded by various experiments. 

 In doing so, our desire has been to assist those who may 

 be almost entirely ignorant of the minutiae of scientific 

 researches, and the difficulties which attend their pursuit. 

 We have attempted first to introduce to the elements ; 

 and, subsequently, to expand to matters of great diffi- 

 culty and importance in some branches of tho art. 



