112 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
According to the author, in alcohol and in fixed and volatile oils 
the Brownian movement is not observable ; it is a property of water 
and of water alone, and is caused by the mutual repulsion of the mole- 
cules of this liquid. 
Mechanics and Optics at the World’s Fair at Chicago, 1893.* — 
Herr B. Pensky and Prof. A. Westphal give an account of the various 
exhibits connected with Mechanics and Optics at the Chicago Exhibition 
of 1893. In these departments the German firms were well to the fore. 
Polished plates of the various kinds of optical glass manufactured at the 
Jena glass-works were exhibited by the firm of Schott and Genossen. 
These included crown glasses, heavy and very heavy baryte-crown with 
high refraction, crown glass with low colour dispersion, phosphate and 
borate glass free from silica, ordinary flint glasses, Jena normal glass for 
thermometers, combustion tubing, &c. The firm of Carl Zeiss was well 
represented by a collection of their apparatus arranged in three divisions. 
The first division contained microscopical apparatus, viz. apochromatic 
and achromatic objectives, compensation eye-pieces, apparatus for ex- 
amining objectives, projection apparatus, photomicrographic apparatus, 
Microscopes of all kinds for biological, crystallographic, petrographical, 
purposes. In the second division were the photographic lenses, in- 
cluding the well-known Zeiss Anastigmatics. The third division showed 
the productions of the firm in optical apparatus intended for physical and 
technical purposes, and included refractometers, contact-micrometers, 
spherometers, focometers, &c., made after the designs of Prof. Abbe. In 
the department of photographic objectives the firms of Steinheil, Yoigt- 
lander, and Schulze and Bartels had extensive exhibits ; the first-named 
firm showed their well-known antiplanatics and their new apparatus for 
telephotography; the firm of Yoigtlander exhibited a number of eury- 
scopics and anastigmatics ; while Schulze and Bartels were represented 
by the teleobjective of Dr. Miette and by a collection of telescopes and 
optical glasses of all kinds. 
In the department of microscopy the firm of Yoigt and Hochgesang 
was prominent with Klein’s Microscope for mineralogical and petro- 
graphical purposes, and with Lehmann’s crystallization Microscope and 
its accessories. The old Berlin firm of Schieck exhibited Microscopes 
for investigations on trichinosis, for entomological and other purposes. 
Important exhibits of spectral, polarization, and photometric appa- 
ratus were made by the firms of Kriiss, and Schmidt and Haensch. The 
first of these firms is responsible for the introduction of the Hefner lamp, 
and the latter for that of the Lummer-Brodhun apparatus in photometry. 
In the mineralogical division of the University Exhibition in the 
German section were exhibited petrographical Microscopes by Fuess and 
by Yoigt and Hochgesang, Klein’s Microscope for more exact minera- 
logical-petrographical investigations, Klein’s heating-Microscope, Nor- 
remberg’s j)olarization-instrument, a collection of Fuess’s mineralogical 
instruments, the crystal refractometer of Abbe, the total-reflectometer of 
Kohlrausch, and many other apparatus. 
England was very poorly represented at the Exhibition. Ross and 
Co. exhibited Microscopes and a number of photographic objectives in 
* Zeitschr. f. Instrumentenk, xiv. (1894) pp. 133-6, 176-80, 210-14, 252-5, 
327-31, 366-9. 
