64 J. C.F. Zoliner on a new Spectroscope. 
very simple method for the attainment of the object in question, 
of the practicability of which I am already convinced by ex- 
eriments on terrestrial sources of light, to be described’ more 
in detail below. The principles on which this method depends 
are the following: 
1, The apparent brightness (glanz, claritas visa)* of a strip 
of a protuberance is independent of the aperture of the slit un- 
der the hypothesis that it continues to have a perceptible 
breadth on the retina. 
2. The brightness of the superposed spectrum increases propor- 
_ tionally to the width of the slit. 
. With an oscillating or rotating slit, the brightness of the 
sions of light, diminishes on the other hand in accordance with 
a law depending on the number and duration of the excita- 
tions of the point of the retina concerned, which oceur in a unit 
of time, and also upon the refrangibility of the strip of the 
protuberance o ed. 
_ If, for simplicity’s sake, we suppose that the entire surface, 
over which the slit moves in its rotation or oscillation, is filled 
we may 
First, reduce the brightness of the image of the protube- — 
rance by an oscillation of the slit, and by this leave unchanged 
the brightness of the superposed spectrum (by 2); or we may 
Secondly, open the slit wnmoved so far that its aperture 
id way, if, 
_ that the intense - of the real body of the sun 
slit. 
= ( pened only just so far that the protuberance 
_ ora part of it may appear in the opening. A suitable weaken- 
