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Akt. 'X.^'K.—Prdceedmgs c^'the Royal Society of Edinburgh i 
(Concluded from VoL VI. p. 37^)* 
March, 18. 1822. ii P. F. Tytleii read the continuation 
of his ‘‘ Biographical Sketches of some of the Earliest of our 
Scottish Lawyers^ 
Ap'i il 1. A paper was read by Richard Saumarez, Esq. en- 
titled, ‘‘ An Inquiry into the Nature Atmospheric Pressure^ 
April 15. A paper by Dr Brewster was read^ entitled, ^^ De- 
scription of a Monochromatic Lamp, with observations on the 
Composition of different Flames^ as modified by Reflexion, Re- 
fraction, and Combustion.'''' 
The chief object of this paper was to describe the principles 
and construction of a Monochromatic Lamp, for. illuminating 
objects with a homogeneous flame, which the author succeeded 
in constructing, after many unsuccessful attempts. By illumi- 
nating microscopic objects with this lamp, a distinctness and per- 
fection of vision was obtained, which extends v*^idely the power 
of the microscope, and enables it to detect delicate structures, 
and minute organizations^ which are beyond the reach of obser- 
vation when common light is employed. The author pointed 
out the application of this lamp to various purposes, both prac- 
tical and scientific, and particularly to the measurement of 
minute optical phenomena^ such as those of refractive powers, 
double refraction, and polarisation, and the phenomena of pe- 
riodical colours* As the yellow light discharged from this lamp 
has an invariable character, the measures of these and other phe- 
nomena, ' taken in such a light by diflerent philosophers, may 
now be referred to as an unchangeable standard, and they will 
also have the advantage of being made in the most luminous 
rays of the spectrum, and of being referable to rays that have 
nearly a mean refrangibility. . 
The author likewise pointed out the manner in which the pris- 
matic spectrum is attacked, and finally extinguished, by the ac- 
tion of diflerently coloured absorbing .media ; and he has, esta- 
blished, in opposition to the deductions of Dr Wollaston ^nd Dr- 
Young, that the yellow light has a separate and independent 
existence in the solar spectrum. 
K 2 
