AAA Miscellaneous Intelligence. 
(3.) When light 7 a _— intensity acts on the eye for a short space 
of time, the brightne the luminous impression on the retina is 
brightness of the light when seen by plas vision; and it is | 
also ascertained that light a pena about the tenth part of a second to | 
avee its full effect on the 
4.) It is found that lights. of “different intensity act on the eye with 
equal rapidity, so that even ‘the light of the sun produces an inpromiae 
with no greater rapidity than that 7 comimon gas flame, 
(6. ) Since Professor Wheatstone’s exporiene me ton proved that the 
light of the electric spark of high tension continues for less than the 
millionth part of a second, and it has been shewn that the brightness of 
the impression, — by light on the eye, increases in the arithmet- — 
ical proportion e time during which it continues to act on si Bed 
na, it follows om ae apparent brightness of the electric spark is 
zo0lso0 Of what it would become if the duration of the spark cou 
_ prolonged to sth of a second. "F rom the great apparent eis 2 
the nearly instantaneous electri¢ spark of high tension, when c ompared 
with the sénsibly continuous light of Voltaic electricity, it is inferred 
that the _brightne ss of electrical light increases with the tension of 
electricit tee 
2, Foster’s Geological Chart, —The following announcement ul 
been received for r publication In this Journal. It affords us pleasure 
know that the Chast’ alluded to has not the sanction of Prof, Mz 
name. 
Ja ékson C, H., Ohio, March 28th, 18 
To the Editors of the American Journal of Science. 
GENTLEMEN,—I received a few days since the March No. of ithe 
Am. Jour. of Science, in which is a notice of Foster’s Geological Chet 
{vide p. 309, vol ix, new series,) saying “+ A revised copy, as a 
for publietion, having the signatures of sarees E. Emmo 
W. Wz. r, has been showmetus by the a 
My name on that Chart is a forgery. ane never seen the C 
have never authorized my name to be put on and pronounce the 
tempt to palm off that production under my signature or recomm 
tion, a base imposition on the public, and a still baser imposition on me. 
[Sign 
3. Lefroy y on the Application , Photography to the Self: registration 
of Magnetical and Meteorological Instruments, (see page 319.)—Mr. 
eka i sent us the following account of bis method of treating his 
mirrors when tarnished.—The mirror will probably be found in course 
of time, to get tarnished and to require cleaning, this may be done with 
soft leather, from which all the dust has been beaten out, and which has 
been well washed in soap and water, and dried before use. If a turning 
lathe is at hand, a convex buff, fitting the mirror, and well covered with 
two or three thicknesses of leather, may be centered on it, and the mirror 
held against it in a support of some kind, while it is made to revolve, but 
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