310 Sir David Brewster's Address 
fluence of Lord Rosse’s example that we are indebted for the fine 
Reflecting Telescope of Mr. Lassels, of which I have already 
spoken ; and it is to it, also, that we owe another telescope, which, { 
though yet unknown to science, 1am bound in this*place espe- 
cially to notice. I allude to the reflector recently constructed by 
Mr. James Nasmyth, a native of this city, already distinguished J 
by his mechanical inventions, and one of a family well knownto | 
us all, and occupying a high place among the artists of Scotland. 
This instrument has its great speculum twenty feet in focal length, : 
and. twenty inches in-diameter ; but it differs from all other teles- , 
“copes in the remarkable facility with which it can be used. its 
tube moves vertically upon hollow trunnions, through which the 
astronomer, seated in a little observatory, with only a horizontal 
motion, can view at his ease every part of the heavens. Hither- 
to, the astronomer has been obliged to seat himself at the upper 
end of his Newtonian telescope; and if no other observer will 
» acknowledge the awkwardness and insecurity of his position, I 
' ean. myself vouch for its danger, having fallen from the very top — 
of Mr. Ramage’s twenty-feet telescope when it was directed to 
‘a point-not far from the zenith. Se ae = 
Seep but slightly connected with astronomy, Teannot omit 
éalling your attention to the great improvements—I may call them = 
te: 
a distinguished member of this Association. The superiority of 
_ the Talbotype to the uerreotype is well. 
the pictures are reverted, and incapable of being multiplied; while 
_ in the Talbotype there is no reversion, and a single negative will 
supply a thousand copies, so that books may now be illu strated 
with pictures drawn by the sun. The difficulty of proetiring good 
paper for the negative is so great, that a better material has been — 
eagerly sought for; and M. Niepce, an accomplished officer in the 
French service, has successfully substituted for‘paper a film of albu- 
“men, or the white of an egg, spread upon glass. Thisnew process 
has been brought to such perfection in this city by Messrs"Ross & 
Thompson, that Talbotypes taken by them and lately exhibited By 
by myself to the National Institute of France, and to M. Niepee, 
were universally regarded as the finest that had yet been execul- 
ed. Another process, in which gelatine is substituted for albu- 
men, has been invented, and successfully practised by M. Poite- 
vin, a French officer of engineers; and by an ingenious method 
which has been minutely described in the weekly proceedings of 
the Institute of France, M. Edmund Becquerel has succeeded 12 
transferring to a daguerreotype plate the prismatic spectrum, with : 
all its brilliant.colors, and also though in an inferior degree, the 
colors of the landscape. These colors, however, are very fuga- 
