20 
The magnificat ions yielded with this objective in conjunction with the 
Hiiyghenian eye -pieces are the same as in the case of the D and DD ; when 
used in combination with the compensating eye-pieces it gives nearly the same 
magnifications as the 4-mm apochroniatic lens of 0.95 aperture (about 9 less). 
The Olbjectiyes a are simple achromatic lenses, so mounted that, notwith- 
standing their great focal length, the body of the microscope remains at its 
ordinary elevation during observation. In the thread is so placed that when 
screwed home the lens is inside the body; it can, therefore, not be used 
with a revolving nose-piece or other objective-changer. They are only intended 
for use with the lower eye-pieces. 
ObjectiYC a* consists of two achromatic lenses combined after a formula 
peculiar to us. By means of a ring rotating like a correction collar the two 
lenses can be approximated or withdrawn, whereby, using one of the lower eye- 
pieces, the magnification is changeable in the proportion from about 1 to 2. This 
graduation of the magnifying power is obviously useful for many purposes. 
We no longer supply the objectives BB, CC; G, K, L (water immersion) 
and ^/g and ^/^g (hom. immers.) of our former catalogues because their special 
aim is now, in our opinion, better realised by the apochromatic lenses. 
All objectives are also supplied adjusted for the 10-inch body and in 
the English form of mount. 
Regarding the use of achromatic objectires in conjunction with com- 
pensating eye-pieces it will be well to state here that only our achromatic 
objectives from DD upwards, i. e. all those having relatively large aper- 
tures should be used in that manner. With those of small apertures the use 
of compensating eye-pieces gives rise to similar errors (though of the inverse 
chromatic order of succession) in the achromatism of the margin of the field 
to those effected when apochromatic lenses are being used in conjunction with 
the ordinary H u y g h e n i a n eye-pieces. 
Separate maho(jany cases for objectives to he L'ept otitside 
the microscope case, with loch, accordim/ to si^e 7 to 30 Marks. 
