8 REPORT 1872. 



In connexion with tlie solution of the most prominent questions connected with the 

 solar envelopes, it may not be without great interest to allude to another point con- 

 clusively decided during the last annular eclipse of the sun, observed by ^Ir. Pogson 

 on the 6th of June of this year, as described by him in a letter to Sir George B. Airy. 

 In 1870 Professor Young was the first to observe the reversal of the Fraiienhofer 

 lines in the stratum closest to the sun. Now, in 1871 doubts were thrown upou the 

 subject. It appears that the reversed lines seem to have been satisfactorily observed 

 by Captain Maclear at Bekul, Colonel Tennant at Dodabetta, and Captain Fyers at 

 Jaifna. The observations of Pringle at Eekul, Respighi at Paodoxottah, and Pogson 

 at Avenashi were doubtful ; while Mosely at Trincomalee saw nothing of this re- 

 versal, which is, according to all accounts, a most striking phenomenon, although of 

 very short duration. Mr. Locli^yer missed it by an accidental derangement of the 

 telescope. The reversal and the physical deductions from it are placed beyond 

 doubt by Mr. Pogson's observations of the annular eclipse on June 6th. At the 

 first internal contact, just after a peep in the finder had shown the moon's limb 

 lighted up by the corona, he saw all the dark lines reversed and bright, but for less 

 than two seconds. The sight of beauty above all was, however, the reversion of 

 the lines at the breaking-up of the limb. The duration was astonishing — five 

 to seven seconds ; and the fading-out was gradual, not momentary. This does 

 not accord with Captain Maclear's observations in 1870, who reports the disap- 

 pearance of the bright spectrum as " not instantly, but so rapidly that I could 

 not make out the order of their going." Professor Young again saj's that "they 

 flashed out like the stars from a rocket- head." But discrepancies in this minor 

 point may be accounted for by supposing ditlerences in quietude of that portion 

 of the sun's limb last covered by the moon. 



The mention of the solar appendages recalls to mind another instance in which 

 photography has befriended the scientific investigator. I allude to the promising 

 attempt which has been made by Professor Young to photograph the protuberances 

 of the sun in ordinary daylight. A distinct reproduction of some of the double- 

 headed prominences on the sun's limb was obtained ; and although as a picture the 

 impression may be of little value, still thei-e is every reason to believe, now that 

 the possibility of the operation is known, that with better and more suitable appa- 

 ratus an exceedingly valuable and reliable record may be secured. Professor 

 Young employed for the purpose a spectroscope containing seven prisms, fitted to 

 a telescope of 6^-inch aperture, after the eyepiece of the same had been removed. 

 A camera, with the sensitive plate, was attached to the end of the spectroscope, 

 the eyepiece of which acted in the capacity of a photographic lens, and projected 

 the image on the collodion film. The exposure was necessarily a long one, amount- 

 ing to three minutes and a half The eyepiece of the spectroscope was unsuitable 

 for photographic purposes, and only in the centre yielded a true reproduction of 

 the lines free from any distortion. A larger telescope, with a suitable secondary 

 magnitiei', will be required in order to secure a more defined image. 



I have hitherto spoken of the successful applications of photography to astro- 

 nomy ; but I must point out also some cases where it has failed. Nebula} and 

 comets have not yet been brotight within the grasp of this art, although, perhaps, 

 no branch of astronomy would gain more if we should hereafter succeed in extend- 

 ing to these bodies that mode of observing them. There is theoretically, and even 

 practically, no real limit to the sensitiveness of a plate. Similarly with reference 

 to planets great difficulties still exist, which must be overcome before their phases 

 and physical features can be recorded to some purpose by photography ; yet there 

 is great hope that the difficulties may be ultimately surmounted. The main ob- 

 stacle to success arises from atmospheric currents, which are continualh' altering 

 the position of the image on the sensitive plate; the structure of the sensitive film 

 is also an interfering cause for such small objects. A photograph taken at Cran- 

 ford of the occultation of Saturn by the moon some time ago exhibits the ring of 

 the planet in a manner which holds out some promise for the future. 



The moon, on the other hand, has been for some time past very successfully 

 photogi-aphed ; but no use has hitherto been made of lunar photographs for the 

 pui-poses of measurement. 



The photographs of the moon are fi-ee from distortion, and offer therefore 



