$9 CTQ 
436 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
(2) Eye-pieces and Objectives. 
. Primitive Fom of Lens-correction.-An interesting old adjusting 
1/8 objective by Andrew Ross, which formerly belonged to Prof. Lindlev 
the second President of this Society (1842, 43), has been presented by his 
son, the Master of the Rolls. It will be remembered that, owing to 
Mr. J. J. Lister s paper on the two aplanatic foci of an objective, published 
Fig. 101. 
in 1836, Mr. Ross was, next year (1837), able to point out that, by means 
of lens distance, the aberration caused by the thickness of the cover- 
lass could be corrected. Two years after this, viz. in 1839, we have 
drawing * of the mechanism by which this correction, or lens dis- 
tancing, was effected ; it will be unnecessary to describe it, as it is 
the ordinary screw-collar actuating the front lens of the objective. In 
* ‘Penny Cyclopaedia.’ Art. Microscope. 
