522 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
surrounding the outlines of all objects in the field of the Microscope, 
when the illumination is obtained by somewhat narrow but sufficiently 
bright beams of light, especially with high powers or deep eye-pieces. 
The latter are true diffraction bands, originating from the diffraction 
of the light at the object, but the difference between the two phenomena 
is that the spectra represent the diffraction effect of the object at a very 
distant plane, conjugate to the posterior focus of the objective, whilst 
the “ bands ” or “ fringes ” show the diffraction effect of the same objects 
in a plane close by, i. e. in the neighbourhood of the objects themselves. 
Nageli and Schwendener, it is true, deny that these fringes are diffrac- 
tion phenomena, and explain them as interference phenomena in a 
somewhat complicated manner, but Prof. Abbe considers that he has 
established the incorrectness of their views on this point, except so far as 
they assert that the phenomena cannot be due to the diffraction effect of 
the lens opening, as had previously been assumed by Helmholtz and others. 
(6) Miscellaneous. 
The 300th Jubilee of the Microscope.* — “ B. C.” writes : — Natural 
science enters this year on a memorable anniversary, the 300th Jubilee 
of the Microscope, one of the most powerful of its resources. To this 
instrument is due in great measure the wonderful impulse given to 
science in the second half of this century. The importance to which 
the Microscope has attained in scientific investigations is well known. 
It has become an absolutely indispensable instrument to the zoologist 
and botanist, to the mineralogist and geologist, to the astronomer and 
the physician. The Microscope has effected a complete revolution, and 
has diverted the direction of study into the most varied channels. In 
fact it has created a new method of research, such as histology. On the 
healing art the Microscope has exercised a most beneficent influence ; 
for while it explained the changes undergone by the finest tissues in the 
various diseases — it was on microscopic observation alone that Virchow 
founded his renowned system of cellular pathology — it pointed out at 
the same time the means of healing them. The Microscope has also 
been of wonderful service in technical matters. Before attaining its 
present high degree of perfection, the Microscope had to pass through 
a number of intermediate stages which it is of great interest to look 
back upon on this its 300th jubilee. . . . 
It is strange how slowly the Microscope found its way into learned 
circles. It was only when Leeuwenhoek had by its aid discovered the 
infusoria that it became generally used in the scientific investigations 
of anatomists and physiologists. What it has accomplished since that 
time constitutes the glory of the natural sciences. The Microscope 
soon passed from the workshops of the spectacle-makers to those of the 
optician, by whose skill it has undergone, little by little, numerous 
changes, corrections, and improvements. Not to mention all of these, it 
will suffice to point out the arrangement of the transmitted light (1685), 
of the reflecting illuminating mirror (1715), aud the use of achromatic 
and aplanatic objective lenses (1824). In more recent times the Micro- 
scope has received further improvements, which have cast into the shade 
all conceivable expectation ; and unless appearances deceive us the finer 
* Central-Ztg. f. Optik u. Mechauik, xi. (1890) pp. 69-70. 
