Apoehromatie Objectives. 
While referring to the paper of Prof. Abbe, entitled "Ueber Verbesserungen 
des Mikroskops mit Hilfe neuer Arten optischen Glases" (Sitzungsberichte der 
Med.-naturw. Gesellschaft zu Jena vom 9. Juli 1H8()) ^) and to the forthcoming 
work of our colleague Dr. Czapski on the "Theorie der optischen Instruniente" 
(Breslau 1893, Trewendt), which combine to furnish a complete exposition of the 
scientific aims and principles which governed the construction of the apoehromatie 
lenses, we must here content ourselves in briefly stating the essential features 
of these lenses. 
These objectives essentially differ from all other microscopical lenses hitherto 
constructed by the simultaneous realisation of the two following conditions: viz. 
1) the union of three different colours of the spectrum in one point of the axis, 
that is to say, the removal of the so-called secondary spectrum inherent to 
the older achromatic lenses, and 2) the correction of spherical aberration for two 
different colours in contradistinction to that for one in the brightest part of the 
spectrum only. 
With all optical systems hitherto constructed, microscopes included, the 
sharpness of the image projected is limited to one particular colour of the light 
transmitted (i. e. green -yellow in the case of lenses used for ocular observations, 
blue-violet in photographic lenses), while the other rays give more or less confused 
images, appearing partly as colour fringes and partly as a general blur. With the 
apoehromatie lenses, however, the projected images are nearly equally sharp for all 
1) Sent gratis on application. 
