J. C. F. Zollner on a new Spectroscope. 67 
and h 
held in the Royal Institution, which ought to appear in print 
that it is most advantageous in observing to bring the length of 
the slit tangent to the sun’slimb. By this plan on the one hand 
a greater segment of the sun’s limb is surveyed at one view, an 
on the other the advantage is gained of determining with great 
accuracy the position angle of the protuberance, since the 
entrance of the sun’s disc makes itself immediately noticeable 
by a flashing out of a narrow band-forme trum i 
order to 
iently before the slit of the spectroscope, two different methods 
an ; ot ths object-glass of the 
ped the position of the slit must be varied in a corresponding 
a revolution of the spectroscope. 
7 the other method, which affords the advantage of an 
unchanged position of the slit, the rays before their union into 
an image are sent through a reversion-prism, so called. If this 
1S rotated about the axis of the instrument, the image of the sun 
also revolves about its center and permits successively different 
ee the limb to fall on the slit. The angle of position is 
‘etermined by the position of the reversion-prism. 
