362 Scientific Proceedings, Royal Dublin Society. 
or a quarter of an hour after leaving a room in which he had been 
exposed to the electric or other bright light. 
Fig. 10. 
nn of 
Of course, when it is desired to concentrate on the slit the 
general light of the sun for examination, a hole in a shutter can 
be used and a siderostat outside. But I refer to these observa- 
tions where it is necessary to form an image of the sun on the 
slit of the spectroscope, and examine each part seriatim, and this 
at present can only be done with an equatorially mounted tele- 
scope, and spectroscope attached thereto. 
