Miscellaneous Intelligence. — 307 
VI. MISCELLANEOUS SCIENTIFIC INTELLIGENCE. 
1, Electric Illumination at Boston,—Photometrical ae of the eh 
(in a letter to Prof. B. Siztimay, Jr, from Prof. Wituram B. Rogers. 
dated Boston, August 14, 1863 oer send you a short account of m my 
purpose were sine in line across the same apartment, commanding a 
range of about fifty feet 
In view of the immense power of the light as observed in the previous 
experiment, I substituted for the 20-candle gas burner, used at that time 
as the standard of comparison, a unit ten times as great, formed by the 
me of a kerosene lamp placed in the focus of a small parabolic re- 
flector and throwing its concentrated light on a photometric screen o' 
prepared paper fixed in front of it, at the distance of five feet. Before 
the observation, the lamp and reflector were so adjusted as to make the 
light cast on ote near side of the screen equivalent by measure to the 
action of 200 ¢ 
This was deus: iy. the intervention of a kerosene lamp fitted up with 
a bridge of platinum wire for defining and restricting the height of the 
square flame. Such a lamp I find of frequent use in ordinary puetcanss 
try, as, when suitably adjusted, it = the light of about eight sta 
candles, and thus transfers the measurement in the photometer to the 
wider divisions of the scale, Being suspended in a balance of 
construction, its rate of consumption enables us to correct for any slight 
departure from the assigned illumination. The lam 
was placed with its flat flame 12 inches ors the screen, while the lamp 
in the reflector was distant 60 inches—and the aa ame of the latter was 
adjusted until the effects on the screen were equalized. 
platform supporting the standard lamp and screen at the 
distance was arranged to slide on a horizontal graduated bar, etoding 
directly towards the carbon points so that the screen should re 
rays from the electric light and from the reflector shesautieclanls on "a 
Opposite faces. In making the observations, the platform was moved to 
judged to be equal, an red distances of the two antago- 
nizing lights the screen - by easy computation their relative 
illuminating power 
By a series of sivals observ: it was found that the carbon light 
had a force varying from 52 to et mes that of the Jamp with bpp 
making it equivalent in alarninatiniy power to the action of 10, 
to 12,000 standard sperm candles pouring their light from the same 
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