TRANS. OF PROF. ABBE’S PAPER ON THE MICROSCOPE. ot 
EXTRACTS FROM MR. HH! E. ERIPP’S 
AICANSLATION.OF PROFESSOR, ABBE’S TAPER 
ON THE MICROSCOPE. 
Monthly Microscopical Journal, vol. xiv. 
CAREFUL consideration of the means at the disposition of the 
optician, and a critical comparison of the difficulties serving as 
a guide to the discussion of the conditions influencing them have 
led me to the conclusion that lenses and systems of lenses of which 
each part has prescribed dimensions, can be executed with an ex- 
actitude that fairly ensures correct action, and with greater facility 
than any other mode of procedure offers for the fulfilment of the 
same conditions with equally good results. 
In the workshops of C. Zeiss, of Jena,* the construction of 
objectives, from lowest to highest power, is regulated by strict 
calculation for each single part, each curve, each thickness of glass, 
each degree of aperture; so that all guesswork and “rule of 
thumb” is avoided. The optical constants of each piece of glass 
are obtained from trial-prisms by means of the spectrometer. Each 
constituent lens is ground as nearly as possible to its prescribed 
dimensions and accurately fitted. In the highest-power objectives 
only is the lens distance left variable, in order that slight deviations 
from accuracy may be adjusted. And thus it has been shown 
beyond dispute that a well-grounded theory, combined with rational 
technical processes, may be successfully substituted for empirical 
practice in the construction of the microscope. 
The fact that an amount of angular aperture, which is unknown 
in any other instrument, comes here into question, renders the ac- 
cepted ideas of “aberration” entirely useless, and the result of 
investigations which were undertaken in order to bring the question 
to some issue, was the discovery that an important feature in the 
optical functions of the microscope had been hitherto overlooked. 
In all previous explanations or interpretations it has been accepted 
as a self-understood proposition that the formation of an image of 
an object in the microscope takes place in every particular, accord- 
ing to the same dioptric laws by which images are formed in the 
telescope, or in the camera; and it was, therefore, tacitly premised 
that every function of the microscope was determined by the geo- 
metrically traceable relations of the refracted rays of light. A 
rigorous examination of the experiences upon which the traditional 
distinction of “defining” and “resolving” powers is founded, has 
shown that the proposition is not admissible. It holds good, in- 
* And we may add, in all the well-regulated workshops in this country. —ED. 
