ZOOLOGY AND BOTANY, MICROSCOPY, ETC. GG1 
tives had shown the same degree of achromatism of the visual light. 
Though it appeared rather strange that Dr. Van Ileurck should not 
have observed the fault, I supposed that he could perhaps have over- 
looked it, or had not found it hurtful, owing to his particular mode of 
illumination or photographic operation. 
“ In this spirit I advised Dr. Czapski to measure the residual differ- 
ence of the chemical focus, and to compute a correcting lens, to be 
added to the system, in order to compensate for the expected difference. 
“ Having left the matter to Dr. Czapski, as I am not versed in 
photomicrography, I was much astonished to hear from him — a short 
time after arrival of the lens — that he could not find a difference of 
focus. In face of the positive assertion about the result of your trial, 
1 felt doubtful about the accuracy of Dr. Czapski’s observation, and I 
requested him decidedly to repeat the trial with all possible precautions, 
though he considered this as useless.” 
Fluor-spar at Oltscheren.* — Dr. E. v. Fellenberg gives a very full 
account of the occurrence at Oltscheren of fluor-spar, which is the 
subject of so much interest to microscopists at the present time. 
Fluorite is a mineral very widely distributed in the Alps. A locality 
long noted for the abundance of the pale-green variety is “ Raun,” or 
more correctly “ Runn,” a wood near Giesbach opposite to Brienz. The 
first mention of this locality is to be found in G. S. Gruner’s 4 Versuch 
eines Verzeichnisses der Mineralien des Scliweizerlandes,’ Burn, 1775, 
and a further description is given in Hopfner’s 4 Mag.tzin fur 
die Naturkunde Hclvetiens,’ vol. iv., 1789, in an account of a journey 
made by General-Commissioner Manuel in the Bernese Alps. Green 
finer was also obtained in the Jura limestone from the Vordendiirr- 
schreunealp am Santis and yellowish-brown and wine-coloured crys als 
from the Upper Jurassic limestone at Saleve bei Genf. But by far the 
most remarkable and interesting occurrence of fluor is that at Oltscheren 
or Oltschialp, more exactly at Oltschikopf, south of the village of 
Brienzwyler in the Bernese Oberland. Here in 1830, according to a 
label on a specimen in the Bern Museum, Hans Fischer and Mitkaften 
discovered in a cleft of the mountain opposite Brienzwyler about 
200 cwt. of fluor, of which 2 cwt. consisted of crystals. These men 
appear to have made considerable journeys with their treasure piled up 
in a cart in huge blocks, some of which, according to Prof. B. Studer, 
who purchased several specimens from them at the time, were a foot in 
diameter, and water-clear like blocks of ice. The precise locality of this 
remarkable find had been forgotten, when in 1886 Prof. Abbe began 
to make inquiries about the occurrence of water-clear fluor-spar. Many 
years before the author had sent to Herr Wappler, a mineral dealer in 
Freiberg, in exchange for Saxon minerals, some water-clear crystals 
of fluor from “das untere Haslithal im Kan ton Bern.” Prof. Abbe 
having seen these specimens was induced to visit the author, by whom 
he was referred to Herr Hamberger, the director of the pyrotechnic 
laboratory in Oberried, near Brienz, as well as to the hunter Caspar 
Blatter, as being the most likely persons from whom information could 
* ‘Ueberden Flusspath von Oltsclurenalp,’ Mittheil. Naturf. Ges. in Bern, 1889, 
pp. 202-19. 
1890. 3 A 
