Mr. J. N. Lockyer on Recent Discoveries in Solar Physics. 1-15 



The first attempt was made in 1SGG, a Herschel-Browning spec- 

 troscope being attached to my telescope ; and the first and many suc- 

 ceeding attempts failed : there was not dispersion enough to dilute 

 the spectrum of the regions near to the sun sufficiently, and as a 

 consequence the tell-tale lines still remained veiled and invisible. 

 Nature's secrets were not to be wrested from her by a coup de main. 



The year 1868 brought us to the now famous eclipse, to see which 

 scientific men hastened from all civilized Europe to India. To this 

 eclipse and its results I need only refer, as they have already been 

 dwelt on at some length in this theatre ; suffice it to say that in the 

 eclipse the spectroscope did its duty, and that the gaseous nature of 

 the prominences was put beyond all question. 



But there was a magnificent pendant to the eclipse, to which I 

 must request your special attention. One of the observers, M. 

 Janssen — a spectroscopist second to none — the representative, in that 

 peaceful contest, of the Academie des Sciences and of the Bureau des 

 Longitudes, was so struck with the brightness of the prominences 

 rendered visible by the eclipse that, as the sun again lit up the scene, 

 and the prominences disappeared, he exclaimed, " Je reverrai ces 

 lignes-la!" and being prevented by clouds from putting his design 

 into execution that same day, he rose next morning long before the 

 sun, and as soon as our great luminary had risen from a bank of 

 vapours, he succeeded in obtaining spectroscopic evidence of the pro- 

 tuberances he had seen surrounding the eclipsed sun the day before. 

 During the eclipse M. Janssen had been uncertain even as to the 

 number of lines he had observed ; but he now by this new method 

 at his leisure determined that the prominences were built up of 

 hydrogen, this fact being indicated by the presence of two bright 

 lines corresponding to the dark lines C and F in the ordinary solar 

 spectrum. 



Let me show you how this result was accomplished, by throwing 

 an enlarged photograph of my telescope and spectroscope on the 

 screen. We have first the object-glass of the telescope to collect the 

 sun's rays and to form an image of the sun itself on a screen. In 

 this screen is an excessively narrow slit, through which alone light 

 can reach the spectroscope. This entering beam is grasped by an- 

 other little object-glass and transformed into a cylinder* of light con- 

 taining rays of all colours, which is now ready for its journey through 

 the prisms. In its passage through them it is torn by each succeed- 

 ing prism more out of its path, till at last, on emerging, it crosses 

 the path it took on entering, and enters the little telescope you see, 

 thoroughly dismembered but not disorganized. 



Instead now of a cylinder of light containing rays of all colours, 

 we have a cylinder of each ray, which the little telescope compels to 

 paint an image of the slit. Where rays are wanting, the image of 

 the slit remains unpainted — we get a black line ; and when the tele- 

 scope is directed to the sun, so that the narrow slit is entirely within 

 the image of the sun, we get in the field of view of the little tele- 

 scope a glorious coloured band with these dark lines crossing it. 

 * Cylindrical, that is, in the case of each pencil. 



Phil. Mag. S. 4. Vol. 38. No. 253. Aug. 1869. L 



