248 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
wanting in clearness, and tliat for a long time he had given up their 
use “ pour quelque genre de travail que ce soit.” Now they are 
forgotten, very few treatises on the Microscope mention them, nor are 
they referred to in catalogues of makers. 
In my preliminary trials I contented myself with adding an objective 
to the existing one, thus making unconsciously a pancratic Microscope. 
But although by this arrangement very curious optical effects could be 
obtained, it was not advantageous for the special end in view, viz. 
convenience of manipulation under the Microscope ; for that purpose 
what could be the use of these foci of indefinite length, or these high 
magnifications which are only obtained by reducing the working distance 
and losing light ? I then conceived the idea of replacing the single lens 
system, giving by simple changes of position all kinds of foci and 
magnification by a series of special systems, each composed of fixed 
lenses, and consequently giving a definite focal length and magnification, 
each system being specially combined in order to produce a definite 
optical effect, and presumably giving more perfect results. Thence 
followed the erecting objectives of long focal length described above. 
If the principle on which they depend is already known, they may at 
least be considered as a new and more practical application. 
The first of these new objectives was constructed by me eleven years 
ago, and was shown then to many persons, amongst whom was M. Verick, 
-who undertook to make similar ones. He did not do so, but his successor 
has been engaged under my direction in this new work. Any maker 
will be able easily to do the same after some trials.” 
The New Apochromatic Objective.* — Dr. J. D. Cox writes : — “In the 
February number of the Boyal Microscopical Society’s Journal we find 
a synopsis of work done with the new apochromatic objective of 1 • 63 
N.A. by Dr. Van Heurck, the distinguished director of the Antwerp 
Botanical Garden. Some references to the same appear in a late bulle- 
tin of the Belgian Microscopical Society. The results mark a positive 
advance in the perfection of objectives, though, as Prof. Abbe warned 
us when announcing the apochromatic lenses which the new Jena glass 
made possible, each step must be a small one in the present state of the 
art, and there are apparently but few more within the range of the 
knowledge and the means possessed by us. 
Now, as heretofore, the study of the diatoms gives the means of 
testing the progress in lens making, and gives the chief stimulus to 
scientific opticians. Dr. Abbe, who has become personally interested 
in the Zeiss optical establishment at Jena, is uniting all the resources 
of scientific formulae with the skill of an almost perfect mechanical 
atelier to produce wider angled objectives; whilst Dr. Van Heurck, 
stepping into the place so long occupied in the microscopical world by 
our lamented Dr. Woodward, of the Army Medical Museum, is, with his 
dark-room and heliostat, demonstrating what the new lenses will do 
upon the old familiar tests of Pleurosigma angulatum, the small Navicula 
rJtomboides ( Frustulia saxonica ), and Amphipleura pellucida. When, 
under his skilful manipulation, real progress is recorded, the improved 
lens quickly finds its way into the hands of the enthusiasts of the school 
Microscope, x. (1890) pp. 164-8. 
