H. W. Wiley—Carbons in the Electric Lamp. 55 
Art. IX.—A Method of Preventing the too rapid Combustion of 
the Carbons in the Electric Lamp; by H. W. Wixky. 
In using the electric light for projections, two chief points 
are to be considered, viz: 1st, brilliancy of illumination, and 
2d, steadiness of the light. When the source of electricity is 
sufficient, the first of these ends is easily obtained. The sec 
ond, however, is not so easy of accomplishment. The chief 
difficulty in the way of securing steadiness is found in the car- 
bons themselves. Some carbons, and I find these to be the 
most common, burn away so rapidly that, where no mechanism 
is present to produce alternating currents, the electric arc is 
constantly passing out of the focus. Often, too, I have found 
that when the current is quite strong with the softer carbons, 
the arc would extend itself momentarily between points as far 
as a centimeter from the end of the carbons. At other times 
it would revolve about the electrodes something like a spiral 
flame in a pyrotechnic display. This leaping and dancing of 
the arc is, of course, fatal to its employment for projection. 
In order, if possible, to remedy these defects in a lantern 
which I have in almost daily use, I made the following experi- 
ments. I first took the specific gravity of three specimens of 
carbon, obtained from different dealers, one in France and two 
in this country. The specific gravity of the French carbon, 
was 1:85; of No. 1, American, 153; of No. 2, American, 
155. The French carbon is hard, of a grayish black color. 
The American carbon is soft, easily broken up, and no 
sign of a metallic luster. The light from the French carbon is 
quite steady and displays very little of that tendency to flicker, 
so troublesome in the American varieties. 
A positive French carbon, which had been used for several 
' hours, until consumed nearly to the lamp, burned away at the 
point, but otherwise retaieoll its original shape. This carbon 
was used without any previous preparation. é 
A soft carbon, however, of the same size as the preceding, 
became red hot to a distance of four to six centimeters from 
the end, and rapidly wasted away ; after being in use for half 
an hour, it was reduced to a slender, tapering form. 
I first tried the plan so well known in France, but so seldom 
tried here, of coating the carbons with a film of copper. The 
precipitation of the copper should take place slowly, and with 
