[87] _Results of Astronomical Observations made during the years 1834-38, at the Cape of Good Hope, &c._ By Sir John Herschel, Bart., K.H., D.C.L., F.R.S.--“In the contemplation of the infinite, in number and in magnitude, the mind ever fails us. We stand appalled before this mighty spectre of boundless space, and faltering reason sinks under the load of its bursting conceptions. But, placed as we are on the great locomotive of our system, destined surely to complete at least one round of its ethereal course, and learning that we can make no apparent advance on our sidereal journey, we pant with new ardour for that distant bourne which we constantly approach without the possibility of reaching it. In feeling this disappointment, and patiently bearing it, let us endeavour to realise the great truth from which it flows. It cannot occupy our mind without exalting and improving it.”--_Sir D. Brewster_: North British Review. [88] For examples of this, consult Graham’s _Elements of Chemistry_; Brande’s _Manual of Chemistry_; or, indeed, any work treating of the science. The formation of ink, by mixing two colourless solutions, one of gallic acid and another of sulphate of iron, may be taken as a familiar instance. [89] Sir John Herschel, in his paper _On the Chemical Action of the Rays of the Solar Spectrum on Preparations of Silver_, remarks that, “it may seem too hazardous to look for the cause of this very singular phenomenon in a real difference between the chemical agencies of those rays which issue from the central portion of the sun’s disc, and those which, emanating from its borders, have undergone the absorptive action of a much greater depth of its atmosphere; and yet I confess myself somewhat at a loss what other cause to assign for it. It must suffice, however, to have thrown out the hint; remarking only, that I have other, and, I am disposed to think, decisive evidence (which will find its place elsewhere) of the existence of an absorptive solar atmosphere, extending beyond the luminous one. The breadth of the border, I should observe, is small, not exceeding 0·5 or 1/7 part of the sun’s radius, and this, from the circumstances of the experiment, must necessarily err in excess.”--Philosophical Transactions, 1840. [90] _Experiments and Observations on some Cases of Lines in the Prismatic Spectrum, produced by the passage of Light through Coloured Vapours and Gases, and from certain Coloured Flames._ By W. A. Miller, M.D., F.R.S., Professor of Chemistry in King’s College, London.--Philosophical Magazine, vol. xxvii.