14 Mr. J. N. Hearder on Electrical Conductivity. 
Mountains. (See the Quarterly Journal of the London Geolo- 
gical Society for August 1856.) 
3. Lepidomelane : a variety of uniaxial mica occurring in small, 
flat, six-sided crystals, of a black colour, in the granite of Three 
Rock Mountain, Co. Dublin. 
This variety of mica contains an unusually large quantity of 
the peroxides and protoxides of iron. 
4. Beraunite, Breit: a variety of Delvauxene, supposed to be 
a hydrous phosphate of peroxide of iron, resulting from the de- 
composition of Vivianite. It has recently occurred at Wheal 
Jane near Truro, in scaly and brittle masses, of a dark brownish- 
red colour, intimately associated with crystallized and decom- 
posing Vivianite, on eisen-nickelkies. My specimens came from 
Mr. R. Talling of Lostwithiel. 
5. Demidoffite : a mineral recently described by Nordenskiold 
as occurring with green malachite, chrysocolla, and phosphate of 
copper, at Tagilsk in the Ural Mountains. It occurs at that 
locality of a pale bluish-green colour, slightly earthy, and coat- 
ing or encrusting the concentric layers of the mammillated ma- 
lachite itself: H. 1-5 to 2-0. In the glass tube, yields water 
with no acid reaction. Composition :— 
Silies 4) PRT Pra Shae 
Alani P's OS SS 
Oxide of copper. . 33°14 
Magnesia. . . . 93°15 
Waters.) iu mee 
Phosphoric acid. . 10°22 
101-62 
Hitherto it seems that this mineral has been only noticed at 
the Russian locality; but I have in my collection characteristic 
specimens, evidently of the same species, from Cumberland, and 
also from a Cornish locality ; as well as from Valparaiso in South 
America, with malachite and muriate of copper. At both our 
British localities it occurs with quartzose rock and malachite— 
the latter, however, not in a mammillated state. 
IV. Extracts from Notes on Electrical Conductivity. 
By J. N. Hearver, Electrician, Plymouth*. 
[T is generally acknowledged amongst electricians that the 
term conduction, as applied to metals, implies negative 
rather than positive qualities; that is to say, all conductors 
afford a certain amount of resistance, but those are considered 
* Communicated by the Author. 
