Ss 
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400 Proceedings of the British Association. 
fixed by gold, by the electrotype process, on the plate, which gives a 
very perfect copy. ‘“‘It would be difficult,” he says, ‘“ to describe in 
words the beauty and perfection of these ‘ copper-tithonotypes.’ The 
problem of multiplying the Daguerreotype may be now regarded as 
completely solved.”-—Prof. Apjohn made a few remarks on this commu- 
nication, which announced results so different from our received ideas 
on this subject, it being generally agreed that the chemical rays were 
the most active in producing the decomposition of the carbonic acid ab- 
sorbed by the plant—Mr. Hunt said, that he had listened with greatsur- 
prise to Dr. Draper’s paper, as, from his own experiments with colore: 
glasses and transparent media, carefully analyzed so as to determine 
what rays were absorbed, and what rays passed through them, he had 
arrived at conclusions diametrically opposed to those now put forth. 
He acknowledged that he had never tried the experiment with the pure 
rays of the prismatic spectrum,: but he should certainly lose no time in 
doing so, on his return to England. 
Dr. Tamnau, of Berlin, exhibited some rare mineralogical specimens: 
1. A group of Datholite from the neighborhood of Andreasberg, in the 
Hartz. 2. Two specimens of rose-colored Harmotome from Andreas- 
berg. The color in these specimens was attributed to the presence of 
a small quantity: of cobalt. ‘They were remarkable for the great size of 
their crystals, which exhibited not only the usual twins, but also curious 
and complicated arrangements of three and four, combined according | 
to laws not yet sufficiently understood to allow of their being clearly 
described. 3. Two very large isolated crystals of Beryl, from Royals- | 
ton, Mass. ‘These were of a beautiful sea-green color, one of them | 
the usual form, a regular six-sided prism, with the direct terminal face. 
The other exhibited the faces of the second six-sided prism, of @ twelve- 
sided prism, and of a twelve-sided irregular pyramid. ‘caine 
“ On the Production and Prevention of Smoke,” by Mr. Henry 
Dircks. Mr. D. thought it important to distinguish between open fires | 
and close fires and furnaces. Open fires would always allow an escape 
of absolute coal gas, and admit atmospheri air to the chimney 3; where- 
as the contrary would be the result with the close fires of the engines 
boiler furnaces. He said that the leading fact of consequence, in refer 
ence to the smoke, was, that it differed materially from the impure gas 
evolved from the coal in the furnace. The plans hitherto adopted by 
manufacturers were chiefly intended to burn smoke, and the great pam a 
ciple of all such plans was to burn the largest quantity of fuel with the 
least quantity of air. The error of this method must appear to every 
one conversant with chemistry. Smoke maybe considered as mere 
carbonaceous matter floating in an atmosphere of the ordinary incom" 
tible products of combustion ; the admission of air to this smoke is of n? 
