434 Miscellaneous Inielligence. 
fering not very much from a circle; by examining which, it will be 
seen, that it gives a counter or corrective aberration, which would make 
the fina emergence nearly, in a beam, parallel to the first incident 
beam first reflected from the outer ring element. Thus the two reflec- 
tions are strongly corrective of each other, and the incident elementary 
beam will emerge, after two reflections, nearly asa true beam, for all 
the extent of vial a field as belongs to high telescopic powers. What 
is true of an elementary beam is equally true of the total beam 
It should be Sead that the rays of each elementary beam lying 
in the plane through its axis and the axis of the cones emerge parallel 
to their first isi and that for the adjacent portions of the ring, the 
lack of accurate emergence would be insensible. Thus, all beaks in 
the field have a perfectly correct defining part, in the ones. 
Another important remark is that all incorrectly condensed ra a are 
) 
the field is the least perfect, but even this has a correct definition, with 
less light, and some overlaying of wandering rays. To what extent 
around the axis the field would prove useful, experiment only can de- 
ide ar as I can judge, this would be fully to the extent required 
in large eb such as are now particularly desired for resolving 
the remote nebulze, and in stellar observation in general. Much of the 
discussion of these mirrors, and their optical actions, I have omitted, as 
ing superfluous here. My general conclusion i in, that optically, this 
condenser is an available means of giving a vast increase to the space- 
penetrating power of telesco 
The loss of light by each rebchian should of course be taken into 
account, as a circumstance lessening the useful effect, in a degree, di- 
ie as oe LAenrption, and dependit ing on the iia iacia! and poli of 
the re lecto 
only meridan observations. To observe at very limited ee 
the meridian, a measureable rotation might be given to the plane mirror 
around its. igh line element, perpendicular to the telescopic axis. If 
