bd 
112 Retiah Association Jor the Advancement of Science. 
therefore, ona grind not purely white, but rendered dusky over 
its whole extent, with one remarkable exception, viz. in that spot 
where the extreme red rays fall, the whiteness of which is pre- 
served, an d- becomes gradually more and more strikingly apparent 
the ictal Mxposirre and the greater the consequent general 
darkening of the paper. 
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The above is not the only singular property possessed by the 
extreme red rays. Their action on paper already discolored by 
the other rays is still more curious and extraordinary. When 
the spectrum is received on paper already discolored slightly by 
the violet and blue rays only, they produce, not a white, but ared 
impression, which, however, I am disposed to regard as only the 
commencement of a process of discoloration, which would be 
complete if prolonged sufficiently. For I have found that if in- 
stead of using a prism, a strong sunshine is transmitted through 
a combination of glasses carefully prepared, so as to transmit ab- 
solutely no ray but that definite red at the extreme of refrangi- 
bility, a paper previously darkened by exposure under a green 
glass has its color heightened from a sombre neutral tint to a 
bright red ; and a specimen of paper rendered almost completely 
black by exposure to daylight, when exposed for some time under 
the same glass, assumed a rich purple hue, the rationale of which 
effect I am disposed to believe consists in a very slow and grad- 
ual destruction, or stripping off as it were, of layers of color de- 
posited or generated by the other rays, the action being quicker 
on the tints produced by the more refrangible rays in props , 
to their refrangibilities. ; 
It seems to me evident that a vast field is thus opened to farsi 
ther inquiries. A deoxydizing power has been attributed to the 
red rays of the spectrum, on the strength of the curious expeti- 
ments of Wollaston on the discoloration of tincture of guaiacum, 
which ought to be repeated ; but in the sensitive papers, and still 
more in Daguerre’s marvellous ioduretted silver, we have re-agents 
so delicate and manageable, that every thing may be expected 
from their application. J. F. W. Herscue. 
Slough, August 28, 1839. 
On the effects of — in three of Her Majesty’s ships, bY 
Mr. Snow Harris. Mr. H. showed from the facts which he hae _ 
_ collected; that were the masts of ships made perfectly good con- 
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