788 PROFESSOR PIAZZI SMYTH ON COLOUR, 
Whence we may easily see, that cobalt-blue glasses are pre-eminent for the 
exceeding redness of the red light they transmit; while ruby-red glasses, the 
very expression for red, for danger-signals, with the public, are low down in the 
scale, and their colour is found to verge more to the spectrum place of orange. 
Tn the case also of the two potassium colours, it is instructive to observe, 
that the pink permanganate is low down or poor in the scale of red, and 
transmits little real red light; while the far bluer, almost slatey blue oxalate of 
chromium and potass is high up on the scale of red, and transmits a band of 
red light which is both splendidly and beautifully red, artistically as well as 
scientifically. 
Somewhat similarly, though with mutatis mutandis, in the search for shades 
suitable to bring out the other faint end of the spectrum, and defend it from 
the brighter middle region, we may here arrange our variously coloured media 
in the order in which they were found to transmit light most nearly up towards 
the lavender-gray end; as thus 
OF ULTRA-VIOLET, OR LAVENDER, AND GRAY, LIGHT, BY 
Wave-number Place of the furthest light transmitted at that end of Spectrum. 








Intensity Newwenar Class of Colour. 
C F : : } of the light Waves at the 
olouring Material, and its depth. at ue ee place in a = "= ae 
Max. —10°0, } British Inch. | orci | chroic. | chrove. 
| Two Blue-lilae glasses, Ora 64 146 be 
Four Cobalt-blue glasses, eal §3 452 x 
Two Red-lilac glasses, . Oat 63 452° x 
100 Judson’s Purple dye, Ors: 62 267 x 
a0 ; Judson’s Violet, Q):75h 61 920 x 
209 Judson’s Ruby, . Vial 61 805 x 
so Ammonia Chloride of Copper, Gia 61 728 x 
ator Permanganate of Potash, 0-1 61 652 x 
zty Judson’s ‘Peach- blossom, 0-1 61, 577 x 
aia ——— Mauvedye, . Oral 61 237 x 
ait Cambridge Blue, On 60 241 x 
sa ——— Oxford Blue, Om 60 241 x 
05 Lavender dye, . O-e 59 916 ae x 
zso7 Litmus Blue solution,. Ong 59 453 x 
a00 Judson’s Green, Ont 54 885 x 
gg Oxalate of Chromium and Potash, : 0-1 53 305 x 
Four stained Green glasses, Ova 50 839 x i 





Where a position at the top of the column exhibits most favour by that 
medium to the more refrangible end of the spectrum. 

