124 
Transactions of the 
fMonthly Microscopical 
L Journal, Sept. 1, 1869. 
carefully ascertained, with special reference to certain lines in the 
spectrum, there will be no difficulty whatever in tracing them 
again, even should they be disguised by the presence of other sub- 
stances. 
So far as I can ascertain respecting the colours of flowers, none 
possess the property of perfectly homogeneous simple colours, as all 
permit more or less of different colours to pass. If any had a 
single colour only, the spectroscope would allow that one to pass, 
while absorption of the rest of the spectrum would occur. Various 
parts of flowers yield differently-coloured solutions, which give 
varying results in the spectrum. 
All coloured solutions appear to have a limit set to their 
dilution; when this is transgressed no reaction is produced on the 
spectrum. This limit may be ascertained by experiment, and test- 
ing the effect on the spectrum. For this reason it is necessary to 
submit various thicknesses or strata of the coloured solutions to the 
micro-spectroscope, otherwise points of interest will be missed. For 
the examination of vegetable fixed oils the test tube should not be 
less than an inch and a quarter in diameter. Density of colour is 
in most cases the guide for the determination of this point. 
If the prisms are not carefully adjusted or arranged, unequal 
dispersion of the spectrum is produced. There is also usually a 
difference between the length and intensity of the bands, generally 
the blue end is twice as long as that of the red ; and although 
narrowing the slit in a measure corrects this, it will not do so 
to any considerable extent. As every part of the band differs in 
refrangibility, the delicate lines produced by some solutions can 
only be brought out by accurately focussing that particular part of 
the spectrum in which they often too faintly appear. 
The rack and pinion motion in the eye-piece must be fairly 
brought into use, and the results observed with artificial light 
should be corrected by daylight. Bands in the red end of ,the 
spectrum are best brought out by artificial light, while those in the 
blue or violet are better observed by daylight. It not infrequently 
happens that with some kinds of daylight admitted into the apart- 
ment its chemical composition is sensibly affected, the Fraunhofer 
line D appears, or even a series of bands which convey delusive 
appearances : this must be guarded against. 
Provision is made in well-adjusted instruments for the correc- 
tion of some of the evils spoken of. It is only proper to say that the 
spectroscope I use is the Sorby-Browning direct vision, which has 
the necessary apphances for obtaining careful adjustment, and is 
in every way the most convenient form of instrument. 
Mr. Browning has, with his usual ingenuity, lately constructed a 
small and portable form of instrument, which can be carried in the 
waistcoat pocket. It is cheap, and can be employed either with or 
