Intelligence and Miscellaneous Articles. 315 
froths considerably when agitated, but the bubbles appear of a pale 
bluish-purple. his is due to the dichromatic character of the liquids 
in question; they admit many rays of the spectrum for a certain 
distance which are afterwards absorbed, and that in such a way that 
the sum of the rays transmitted by the thin stratum conveys to the 
observer a different impression of colour to that which is conveyed by 
those rays which can penetrate a thicker stratum. Thus the thin 
film of cochineal solution which constitutes a bubble transmits the 
red ray, a yellowish-green ray, a bluish-green ray, and nearly the 
whole of the blue and violet of the spectrum; the resulting colour 
is accordingly bluish-purple mixed with much white light: a thicker 
stratum of the same cuts off both the green rays, and a still thicker 
one transmits only the red. 
Of a similar nature is an appearance observed in port-wine. The 
new wine, when shaken, forms a bubble which is faintly red, while 
old port forms one that is colourless. This, indeed, is sometimes 
taken advantage of as an indication of the age of port. The differ- 
ence arises partly from a gradual change that takes place in the 
colouring matter of the wine, partly also on the diminished thick- 
ness of the film that constitutes the bubble of the older and ‘thinner’ 
wine. If old port be placed in a hollow glass wedge, and thus in- 
terposed between the eye and a slit in the window-shutter in such a 
way that the line of light is seen traversing the different thicknesses 
of the liquid, that line will appear white where the stratum is thin- 
nest, and will become red very suddenly as the stratum increases ; 
almost as intensely red, in fact, as when the thickness is considerable ; 
and if this line of light be analysed by a prism, it will be seen that 
every ray of the spectrum traverses the thin stratum, but that sud- 
denly they are cut off, all at very nearly the same distance, with the 
exception of the red ray and a portion of the orange, which are 
transmitted through almost any amount of the liquid. 
Some bubbles, as is well known, exhibit that beautiful phzeno- 
menon designated ‘the colours of thin plates,’ or ‘ Newton’s rings.’ 
This is most strikingly displayed by the froth on the surface of the 
black liquid produced by adding a few drops of sulphuric acid to oil 
of turpentine: the play of colours is beautifully relieved against the 
black background. 
NOTE ON CAPILLARY ACTION. BY G. WERTHEIM. 
The theory of capillarity rests upon the hypothesis that the volume 
of liquid which is raised above the level is in proportion to the con- 
tour of the section of the solid wall, whatever may be the curvature 
of this contour. This hypothesis, enunciated by Laplace and coin- 
cident with that of Young, serves as a point of departure from which 
we descend to the development of all particular cases, and rise on the 
other hand to the study of molecular forces. It cannot therefore be 
too carefully verified; but unfortunately the integration of the fun- 
damental differential equation is only capable of being effected in 
