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LXII. Onthe Tithonotype, or Art of multiplying Daguerreo- 
types. By Joun Witi1AM Draper, M.D., §c.* 
1. JN a paper “On the Action of the Rays of the Solar 
; Spectrum on the Daguerreotype Plate,” inserted in 
this Journal for the month of February 1843, which has just 
reached me, Sir John Herschel points out that a connexion 
may be traced between the phenomena of coloration im- 
pressed by the spectrum, and those of Newton’s rings. With 
striking ingenuity he shows how a succession of positive and 
negative pictures may arise by prolonged solar action, and 
those shades of colour which the iodide of silver exhibits, un- 
der variable exposure to light, originate. 
2. This hypothesis, however, as that able philosopher pro- 
ceeds to state, is not unattended with difficulties, and after 
" pointing out what those difficulties are, he shows how neverthe- 
less it can account for an extensive group of facts. I regret 
that these difficulties are in the way, and that there are also 
other facts which appear to exclude the theory of thin plates 
from these phenomena. 
3. The Daguerreotype image in all its forms may be trans- 
ferred by any copying process to other suitable surfaces. In 
other words it may be printed from. 
4. Sir D. Brewster was the first to show that the colours 
of mother-of-pearl might be impressed on any yielding sur- 
face. In the same manner so can the Daguerreotype image. 
5. This is unquestionably the most important fact yet known 
in the history of these mysterious images, both in a theoretical 
and in a practical point of view. In a theoretical point of 
view, it shows us that it is among the phenomena of grooved, 
or striated, or dotted surfaces that the Daguerreotype is to 
be ranged, and in a practical point of view it shows the true 
mode of solving the great problem of producing from a given 
proof a multitude of copies. 
6. In this Journal for September 1841 (p. 202. (37)), in 
speaking of the action of isinglass dried on the surface of the 
Daguerreotype pictures, I stated that I had succeeded with a 
process for multiplying copies, and promised on a future oc- 
casion to make it known: that promise I now proceed to res 
deem. 
7. On referring to the paper in question the reader will 
perceive that the following facts are stated (p. 199 (20.)), that 
gum-arabic mucilage, dried on a common Daguerreotype, 
splits up bringing with it the white portions: that Russian 
* Communicated by the Author. 
