782 PROFESSOR PIAZZI SMYTH ON COLOUR, 
rather than representations, of prism-observed phenomena have monopolised 
attention among the greater spectroscopists.* — (See also p. 842.) 
COLOURED FLUID SERIES. (See also Plate 2, No. 42 of this Vol.) 
The number of colours offered by commercial glass, being very limited, I 
next tried watery solutions of various well known chemicals, including a list of 
aniline dyes as prepared for the people by Mr Jupson; and tried most of them 
at three, and some at six, different strengths. 
In this manner there were examined altogether of 
REDS, twelve; with notes on a few more; 
YELLOWS, four; 
GREENS, two; 
BLUES, four; and 
VIOLETS, five. 
The individual observations are contained in their numerical printed form 
in Appendix IT., pp. 816 to 842; and the first medium operated on, potassic 
permanganate, had several of its stages given by duplicate observations, to 
afford some idea of the amount of probable error in any single observation 
further on. 
The graphical representation of all the more important of the above obser- 
vations is given in MS. Plates 4 to 14 (reduced, for economy, to one engraved 
Plate, No. 2); in the order above indicated from Red to Violet and Lavender- 
Gray; the spectrum projection being the same as that already explained. (See 
also p. 842.) 
FIRST RESULT, from both glasses and fluids. 
The first general result to be drawn from all the observations is that,—the 
luminous bands left outstanding in these so-called absorption spectra of colour- 
ing materials are moveable in the spectrum with variation of the depth of 
the colour medium. For an increase of such depth invariably makes a red band 
move further to the red, and a blue band further to the blue, end of the Spec- 
trum. There can therefore be no coloured glass ever depended on either to stop, 
or transmit any one mono-chromatic ray alone; for the said glass will act some- 
times on one, and sometimes on another and neighbouring spectral ray, according 
to the temporary brilliance of the light, and depth of colouring matter. 
This notable point was first ascertained by the varying micrometer measures 
* Further, we place the red-end, or natural beginning, of the spectrum to the left-hand because, 
although a recent reviewer of Mr Rand Capron’s “ Photographed Spectra” chides him for so doing; 
and says, “have not Kirchoff, and Huggins placed the red-end to the right;”—-yet the opposite plan 
has been adopted by Fraunhofer, Brewster, Gladstone, Bunsen, Janssen, Roscoe, Watts, De Willengen 
per Secchi, Plucker, Hittorf, De Boisbaudran, and lastly Russell of Sydney in the “ Observatory” for 
March 1879. While we may also claim the practice of the whole European family of nations in 
writing from left to right, never from right to left.—(Added March 8, 1879.) 

