336 THE BEGINNINGS OF PHOTOGRAPHY. 



In an index at page 702 of this ])ook we find tlie German equivalents 

 to the Latin names of a number of ores of silver, but thei'e is no men- 

 tion wliatcver of horn silver, nor have I found any distinct reference 

 to it in the volume. Nor is there any reference to the darkening of 

 these ores by light, though he says of one form of Tyrolean glassy 

 ore (argentum rude rheticum, pri)l)ably a sulphide*) that from a blue 

 inclining to violet "it blackens or is ash colored. 



FARRICIUS AND OTPIERS ON HORN SILVER. 



In a note to a memoir on Daguerreotype, written about 1839. Arago 

 says (OEuvres completes, T, 4»)t)) that in a work l)y Fabricius (De Rebus 

 Metallicis, 1.5.56) there is a full description of a kind of silver ore called 

 "horned silver," with the color and transparence of horn, the fusibility 

 and softness of wax. Exposed to light, it passed from a 3'ellowish 

 gra}^ to violet, and by a more prolonged action became almost black; 

 it was natural horn silver. Tissandier (History and Handbook of 

 Photography) makes Fal)ricius an alchemist and says that he prepared 

 luna cornea by precipitating a solution of silver nitrate with sea salt, 

 and that in his Book of the Metals (15.56) he relates that the image 

 projected by a glass lens onto a surface of luna cornea imprinted itself 

 in black and g'ray according as the parts were completely illuminated 

 or touched only by diffused light. Harrison, in his History, also 

 gives a simihir account. 



Becquerel, Eder, and Fabre have already noted that there is nothing 

 to this effect in the little treatise De Metallicis Rebus ac Nominibus, 

 ohservationes variie et eruditfe, ex Schedis Georgii Fabricii: (juibus 

 ea potissimum explicantur, qn&i Georgius Agricola prwteriit, com- 

 piled from notes by (jeorgius Fabricius (Georg Goldschmied) sent b}- 

 his brother to Kentmann and published in 1566 b}^ Conrad Gesner, of 

 Zurich, in a collection of simihir treatises on gems, fossils, minerals, 

 etc. In the chapter on silver (p. 6) Fabricius sa3^s: "In no metal is 

 there such a great variet}' of colors as appears in this by some marvel- 

 ous artifice of nature: some ores are transhicent, as the red or liver- 

 colored, another is like a ruby, a third lias a horny light (hicem cor- 

 neam) and is very like cornelian (sarda)." Again he says that "the 

 liver-colored ore is described in his book of metals (in nostra corpore 

 metallico). This also is soft like lead and melts over a candle; poured 

 out on gy])sum, on account of its spiritual subtility it is entirely con- 

 sumed. Its thinner particles are translucid like horn, the thinnest 

 like ice." In a list of various ores of silver (p. lo) lie mentions one 

 (cornei coloris translucidum), ti'anslucid Avith the color of liorn, but 

 that is all; not a word al)out any change of color by exposure to light 

 or otherwise. From the above it seems possible that Fabricius wrote 

 an earlier work on metals, ])ut I have not been able to find any trace 

 of it. From 1553 till his death, in 1571, he was director of the college 



