586 Chronicles of Science. [Oct., 
certain parts of the Taunus range in Western Germany, but it 
seems doubtful whether it should take rank as a distinct mineral. 
The author recognizes two varieties—the one fibrous, with a satiny 
lustre; and the other lamellar, with a metallic lustre: the latter is 
of younger formation than the former. 
A new species discovered in the copper veins of Nantoko, in 
Chile, by Herr Herrmann, has received the name of Nantokite.* 
In its pure condition it is a perfectly anhydrous chloride of copper, 
but by exposure to the action of atmospheric influences it becomes 
converted into atacamite. 
Another new species is to be termed Helvatane, from its occur- 
rence in the Alps of Switzerland. It is apparently a felspathic 
mineral, found in the mica-schist of the Todi Mountains.+ 
Two closely-allied minerals have long been known under the 
names of Leadhillite and Susannite. They occur together in the 
old mines of Lead Hills in Lanarkshire, and they possess precisely 
the same chemical composition,—both being sulphato-carbonates of 
lead. lLeadhillite crystallizes, however, in the rhombic system, 
whilst Susannite affects hexagonal forms. Dr. Kenngott has 
lately examined these crystals with care, and believes that the 
apparently hexagonal forms of Susannite are purely deceptive, 
arising from the twining together of crystals of Leadhillite, just 
as the rhombic crystals of Witherite become twinned in pseudo- 
hexagonal forms. 
10. PHYSICS. 
Licut.—Professor H. Morton, of the University of Penna, has de- 
vised a very ingenious arrangement for obtaining monochromatic 
light of considerable intensity. The difficulty which there has 
hitherto been in producing monochromatic light in great quantity 
prevents us from demonstrating satisfactorily many points of in- 
terest in connection with the composition of light and the theory of 
vision. Coloured glasses placed in the path of powerful beams of 
white light are doubly unsatisfactory ; they reduce the amount of light 
enormously, and with few exceptions (e.g. red glass coloured with 
gold) yield a beam of mixed colour. The old experiment, the 
spirit-lamp with salted wick, is admirable as far as it goes, but 
yields a very faint light at best. Something far superior to this is 
furnished by the arrangement of a ring of cotton wick wound on a 
wire, and supported immediately over and around a large Bunsen 
burner, the wick being soaked with an aqueous solution of some 
* ‘Berg-und hiittenmann. Zeitung,’ XXVIL., No. 1, p. 3. 
+ ‘Neues Jahrbuch,’ Heft IIL, p. 348, 
} Ibid., p. 319. 
