THE LliSTJS OE THE SOLAE SPECTEHM. 
151 
The green space between E and F was made the object of special study, and a sepa- 
rate map of it on a scale twelve times that employed by Feaunhofer is given in fig. 4, 
while %. 6 represents, on a still larger scale, the lines included within what is ordinarily 
denominated the triple line h. 
The blue space between F and G is that of which the delineations appear the least 
trustworthy ; indeed there is some discrepancy among the drawings of the lines between 
F18 and F27. The violet space from G to H is probably deserving of greater con- 
fidence. The sparse lines beyond H seem to extend to the further limit of Becquerel’s 
group L, which, with the group I, is faintly indicated. 
In the summer of 1858 Dr. Gladstone examined the two extremities of the solar 
spectrum where Fraunhofer’s map is manifestly deficient ; and as these are the portions 
where there is least light, he made his observations on very bright days about midsummer, 
and at noon, consequently when the sun was at about its highest in the latitude of 
London. The instrument of the Bev. Baden Powell, described and figured in the 
British Association Report for 1839, was employed, and a good prism of flint-glass 
haring an angle of 45°. The light of the sun was reflected from the quicksilvered 
mirror of a heliostat ; and a blue cobalt glass was placed in front of the eyepiece of the 
telescope. This latter precaution is necessary in order to intercept, or greatly reduce 
in brilliancy, the orange, yellow, and green rays ; for although the telescope takes only 
a part of the prismatic image into the field of riew at a time, it will still happen that, 
however pure the glass of the prism may be, and however carefully cross-lights are pre- 
vented, some of the middle rays will be irregularly dispersed, and will mix with the red 
or lavender ; and when the sun is shining brightly into the instrument, these rays will 
be in sufficient quantity to render it a matter of great importance that they should be 
stopped by cobalt glass. The results of these observations are given in fig. 6, which is 
on the same scale as Fraunhofer’s spectrum, or one-fourth of that adopted in fig. 1. 
From this map it is evident that the appearance of lines and bands between A and B 
is not confined to periods of the day, or latitudes, where the sun is at no great height 
above the horizon, although none, except the group a, are delineated in the Munich 
diagram. It will presently be seen, however, that they become much more visible when 
the sun’s light traverses a larger portion of our atmosphere. Light was perceived by 
Dr. Gladstone for a considerable space anterior to A, but no lines were distinguishable 
in it, on account probably of the inferiority of his apparatus to that employed by Sir 
David Brewster, whose drawings also had not been seen or heard of by him when he 
made these observations. 
On comparing this map in its delineation of the rays beyond H with the drawings of 
M. Becquerel* and Professor Stokes f, it will be at once evident that it contains the 
lines marked by them as far as it extends, besides many finer ones. Yet the three 
maps represent three different phenomena: that of Becquerel the lines and spaces 
where there is no chemical action ; that of Professor Stokes the lines and spaces where 
* Bibliotheque TTniv. de G-eneve, xl. t Philosophical Transactions, 1852. 
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