February 1, 1897.] 



KNOWLEDGE. 



35 



Spanish eclipse of July 18th, 1860, to depict the " red 

 prominences," the mere display of which, as progressively 

 covered on one side and uncovered on the other by the 

 moving globe of the moon, sufficed to demonstrate their 

 solar dependence. A daguerrotype of the corona of 1)S51 

 is still extant ; and coronal photography has grown to be 

 an art in itself, practised, weather permitting, with added 

 success, each time that the mysterious solar nimbus starts 

 into view from behind the interposing moon. It imprinted 

 itself with particular effectiveness on plates exposed by 

 Sir George Baden Powell at Novaya Zemlya, August 9th, 

 1896. The instructive details of its intimate structure 

 can be studied only by means of such authentic records. 

 A photograph of the " reversing layer," fortunately secured 

 on the same occasion by Mr. Shackleton, locates the chief 

 seat of the Fraunhofer absorption in a shallow stratum 



1892 and 1894 several minor apparitions were photo- 

 graphed by Prof. Barnard night after night, with the 

 " Willard lens " of the Lick Observatory. The multiple 

 nature and fibrous composition of their tails, imperceptible 

 telescopically, came out strikingly upon his negatives, which 

 testified besides to irregular effluxes of nebulous matter 

 from the heads. 



Dr. Henry Draper obtained a promising photograph of 

 the Orion nebula, September rtOth, 1880 ; and Dr. 

 Common's classic pictures of the same object, by which 

 the future of nebular self-delineation was assured, followed 

 in 1883. Dr. Roberts next entered a field in which he has 

 won signal success. A plate exposed for three hours, with 

 his twenty-inch reflector, October 1st, IhHh, disclosed the 

 Andromeda nebula in its true annular or spiral shape — 

 furrowed, as it were, by the action of some mighty 



Vienna Obsektaioet : an Ideal Establishment surH as we mi9ht have, but have not, in England. 



near the photosphere. The phenomenon had been spec- 

 troscopically viewed as a flash of bright rays by Prof. 

 Young in 1870. 



Comets and nebula are slow in self-portraiture ; which 

 was, indeed, rendered practicable only by the invention of 

 dry plates with their attendant facility for long exposures. 

 Hence, the first comet successfully recorded was Tebbutt's 

 .in .June, 1881 ; while some photographs of the great 

 September comet of 1882, obtained by Mr. Allis at the 

 Cape Observatory under Dr. Gill's supervision, started 

 and exemplified two broad streams of laborious inquiry. 

 Taken with a common portrait-lens, their perfection 

 showed the advantages of the wide field of view and 

 strong concentration of light afforded by that type of 

 instrument ; and the richness of their star-sprinkled back- 

 grounds irresistibly suggested the use of the camera for 

 ,the preparation of stellar charts and catalogues. No 

 .brilliant comet has appeared since 1882 ; but between 



unknown force. The same formative law is operative in 

 many sidereal bodies. Whorled nebul* were recognized 

 visually, with the Eosse six-foot reflector, in 1810 ; their 

 mode of structure has been ratified and extended by the 

 camera. Even the immense southern aggregations of 

 stars and nebuhe known as the Magellanic Clouds, appear, 

 from Mr. Kussell's photographs, to have their parts disposed 

 along helical lines. This is wonderful and inexpHcable. 



Prof. Barnard undertook in 1889 the task of photo- 

 graphing the Milky Way. It is not an easy one. The 

 star-clouds and star-sprays constituting it can neither be 

 seen nor depicted with an ordinary telescope. They must 

 be taken in the mass, not bit by bit. The Willard lens, 

 however, proved equal to the occasion, and a series of 

 astonishing galactic views were produced, in which lucid 

 piles and drifts of star-dust are singularly interrupted by 

 black chasms, cracks, and vacuities. 



The plan of multiple exposures, introduced by Dr. 



