XCvi REPORT — 1869. 



showed, not exactly, with D. The bright linos coinciding with C and F 

 indicate the presence of glowing hydrogen. 



This is precious information to have gathered during the brief interval of 

 the total phase, and required on the part of the observers self-denial in with- 

 drawing the eye from the imposing spectacle of the surrounding scenery, and 

 coolness in proceeding steadily with some definite part of the inquiry, 

 when so many questions crowded for solution, and the fruits of months of 

 preparation were to be reaped in three or four minutes or lost altogether ; 

 especially when, as too often happened, the observations were provokingly 

 interrupted by flying clouds. 



But valuable as these observations were, it is obvious that we should have 

 had long to wait before we could have became acquainted with the .usual 

 behaviour of these objects, and tlieir possible relation to changes which may be 

 going on at the surface of the sun, if we had been dependent on the rare and 

 brief phenomenon of a total solar ecHpse for gathering information respecting 

 them. But how, the (juestion might be asked, shall we ever be able so to 

 subdue the overpowering glare of our great luminary, and the dazzling 

 illumination which it produces in our atmosphere when we look nearly in its 

 direction, as to perceive objects which are comparatively so faint ? Here 

 again the science of optics comes in aid of astronomy. 



When a line of light, such as a narrow slit held in front of a luminous ob- 

 ject, is viewed through a prism, the light is ordinarily spread out into a 

 coloured band, the length of which may be increased at pleasure by substitu- 

 ting two or more prisms for the single prism. As the total quantity of light is 

 not thereby increased, it is obvious that the intensity of the hght of the 

 coloured band will go on decreasing as the Iwigth increases. Such is the case 

 with ordinary sources of light, like the flame of a caudle or the sky, wliich 

 give a continuous spectrum, or one generally continuous, though interrupted 

 by dark bands. But if the light from the source be homogeneous, consisting, 

 that is, of light of one degree of refrangibility only, the image of the slit 

 win be merely deviated by the prisms, not widened out into a band, and not 

 consequently reduced in intensity by the dispersion. And if the source of 

 light emit light of both kinds, it will be easily understood that the images of 

 the sht corresponding to light of any definite refrangibiUties which the mix- 

 ture may contain wiU stand out, by their superior intensity, on the weaker 

 ground of the continuous spectrum. 



Preparations for observations of the kind had long been in progress in the 

 hands of our countryman Mr. Lockycr. His first attempts were unsuccessful : 

 but undismayed by failure, he ordered the coiistruction of a new spectroscope 

 of superior power, in wliich he was aided by a grant from the sum placed annu- 

 ally by Parliament at the disposal of the lloyal Society for scientific purposes. 

 The execution of this instrument was delayed by Avhat proved to be the last 

 illness of tbe eminent optician to -nhom it had been in the first instance en- 

 trusted, the late Mr. Cooke ; but when at last the instrument was placed in his 

 hands, Mr. Lockyer was not long in discovering the object of his two years' 

 search. On the 20th of October last year, in examining the space immediately 

 surrounding the edge of the solar disk, he obtained evidence, by the occiirrence 

 of a bright line in the spectrum, that his slit was on the image of one of 

 those prominences, the nature of which had so long been an enigma. It 

 further appeared from an observation made on November 5 (as indeed might 

 be expected from the photographs of Mr. De La Eue, and the descriptions of 

 those who had observed total solar eclipses) that the prominences were merely 

 elevated portions of an extensive luminous stratum of the same general cha- 



