508 



Lieut. J. Herschel on Spectroscopic [June 17, 



The position of e is estimated ; for there are no visible solar lines between 

 B and C (in my spectroscope), and because by the time I was ready to go 

 back and measure it (4" having already faded) it was no longer to be seen ; 

 and as the other lines had visibly decreased in brilliancy, I could only con- 

 clude that I had been a fortunate witness of the effects of a violent and 

 spasmodic action or eruption of vapour lasting only a few minutes. Nor 

 did I see any recurrence of this spectacle, though I watched for some 

 time. 



I should here state that I was looking at this time at a very low stratum, 

 and that the line 7 is rarely visible except quite close to the sun's limb ; 

 F also is not generally brilliant, except near the limb. B is never (so far 

 as I have seen) so brilliant as either C or F. 



I have said that these appearances are to be seen without any defence 

 from excessive light ; and this is strictly true, for I have seen them rea- 

 dily, even when the paper cap which I at first used over the object-glass 

 was removed ; but as a precaution against the heating-effects of the sun's 

 image, I have latterly used metal diaphragms, one of ^-inch diameter, 12 

 inches, and a second of |*-inch diameter, 1^- to 2 inches distant from the 

 slit. When these had been inserted I dispensed with any cover for the 

 object-glass. I was in hopes that, by carefully stopping out all unneces- 

 sary light in this way, I should be able to dispense with a slit, and view the 

 monochromatic images of a protuberance on the white background (so to 

 speak) of the atmospheric illumination. But so far I have been disap- 

 pointed. Nevertheless I still believe that whoever will go a step further 

 and use a red glass prism without a slit will see the actual "red flames." 

 [When writing my eclipse-report I was under the impression that the 

 orange was the principal light (v. § 43).] This much of foundation I 

 have for this belief, that I actually have seen the form of a solar cloud 

 through a widely distended slit — not a luminous line of varying length and 

 position, but a view such as you may obtain through a partly open shutter 

 by moving the head slightly to and fro, only that the movement was in 

 this case effected by a gentle pressure up and down of the telescope itself— 

 a movement rendered possible by the absence of perfect rigidity of the in- 

 strument. In this way I could see clearly that the solar clouds were very 

 similar to terrestrial ones, fleecy, irregularly shaped, and illuminated, &c, 

 just as eclipses have told us they are. The opening through which I 

 viewed them was about \ of a minute in width, and the height and length 

 of the mass \\ and 3 minutes respectively, or thereabouts. 



After this I need not describe the appearances of the lines, the less so 

 as I fully expect that, once the ready visibility of these appearances be- 

 comes realized, numerous accounts of such eruptions as I saw yesterday, 

 as well as of the real forms and appearances which they present, will be 

 forthcoming from observers who can better spare the necessary daylight 

 hours. 



* This is too large. 



