1861.] on De la Hues Photographic Eclipse Results. 365 



This had the effect of rendering visible a little more of the prominences 

 on the northern limb, and of shutting off a portion on the southern 

 limb of the sun. 



The speaker drew attention to the heights of many of the pro- 

 minences ; to the circumstance of their brilliancy in some cases being 

 greatest in those parts nearest the sun, while in others the brightest 

 part was on that edge most distant from the sun. One prominence, 

 upwards of 70,000 miles distant from the sun's limb, was particularly 

 pointed out — this had not been seen by human eyes, but there was its 

 image fixed and recorded by the heliograph in both the pictures. 

 Photography could therefore render evident to us phenomena of the 

 sun which the human eye could not discern ; and here we had another 

 of the many proofs of the importance of varying our means of observa- 

 tion. This prominence was not the less real because we could not see 

 it ; it existed and emitted a radiant force ; invisible it was true, but still 

 nevertheless a force, and even possibly a greater chemical force than 

 that of the visible prominences. In order to render this apparent, a 

 spectrum was produced by means of the electric light and projected ou 

 to a collodion plate recently made sensitive, and placed in full view of 

 the audience ; during the thirty seconds of exposure, marks were made 

 by scratching through the collodion film to indicate the position of red, 

 yellow, green, and violet bands ; on developing the picture and pro- 

 jecting the image on to the screen, it was seen, by reference to the 

 scratches, that up to the violet band very little effect had been pro- 

 duced, but that the invisible rays beyond the violet had produced a very 

 intense image, to an extent equal to the breadth of the visible spectrum, 

 consisting of several well-marked bands of varying intensity. 



The speaker now drew attention to the corona : on Mr. De la Rue's 

 photographs the corona to some extent was visible, but recourse was 

 had to a photograph of a drawing showing the whole phenomena, which 

 was also projected against the screen. It was pointed out that observa- 

 tions in Spain had proved that the corona polarized light, and as light 

 coming direct from a luminous body is not polarized, but that after 

 reflection it is so ; the fact of polarization tended to show that the 

 corona must be a consequence of an atmosphere around the sun reflect- 

 ing the sun's light. 



The speaker concluded by drawing attention to some phenomena 

 connected with the sun's spots, their rotation, the sudden bursting out of 

 a brilliant light observed by two astronomers distant from each other ; 

 and also to a curious foliated appearance in the sun's spots, observed by 

 Mr. Nasmyth. What are these vast masses which reach to such 

 enormous distances beyond the sun, as we see him under ordinary cir- 

 cumstances ? One, we perceive, extends nearly as far from the sun as 

 three times the entire circumference of the earth, and another is sus- 

 pended away from the sun's limb about once that distance ! Modern 

 science places at our disposal methods of determining the nature of 

 some of the constituents of the sun's atmosphere, with a degree of cer- 

 tainty equal, perhaps, to any of our laboratory methods, could we bring 



