278 Scientific Proceedings, Royal Dublin Society. 
that is absolutely essential for the best work. These two objections 
practically dispose of the first method ; and the rotation of the corona 
introduced by the second method is a serious objection. 
The chief objection to Professor Scheeberle’s plan is that the 
image of the sun travels across the field of the object-glass during 
the eclipse, and that it is only at mid-eclipse that the plate is 
exactly in the optic axis of the object-glass. As the movement of 
the sun in 3 minutes of time is about 45 minutes of are, and the 
field of a good object-glass is practically perfect over at least 2°, 
and very good for 1° on each side of this, this objection is not a 
serious one, for we could rely on getting good definition during 
a 6 minutes eclipse, and we rarely get such duration for these 
phenomena. ‘The only moving parts in this arrangement are the 
plate-carrier and plate, and these are extremely light, so that very 
perfect motion can be given by a very simple clock, or by some 
simple water-motor similar to that adopted by Professor Hale, of 
Chicago, in his spectroheliograph. With the apparatus used in 
Chili Professor Schceberle gave exposures of 32 seconds, and 
obtained perfect pictures. The instrument of the future for 
obtaining the inner and middle corona at eclipses will probably 
be some simple apparatus founded on this principle, in which a 
long-focus object-glass will be used, and small photographic action 
obtained on the plate. 
