24 
Aeeessory Apparatus 
for testing the fundamental properties 
of Mieroseopieal Objectives. 
No. 
*Apertometer after Abbe, for estimating the numerical and 
angular aperture of objectives (Journ. of the R. Micr. Soc, Jany. 
1878, p. 19, and 1880, p. 20). For use on any large stand fitted 
with a draw tube. Including the auxiliary objective, in case 
(lig. 2) with directions 
Fig. 2. 
Apertometer. 
*The same apparatus, glass disc, mounted on metal plate 
with a slot for the adjustment of the indices 
