Definition of "scintillation"

Do the stars scintillate at all altitudes? Is there any altitude at which it ceases to manifest itself? At Morges the stars in general scintillate at all altitudes, although feebly near the zenith; but on the nights when the scintillation is very faint, it ceases completely at a zenith distance of 45°.

1857 December 11, Charles Dufour, “Notes on the Scintillation of the Stars. By Professor Dufour. (Extracts of Letters to Professor Piazzi Smyth.)”, in Monthly Notices of the Royal Astronomical Society, Containing Papers, Abstracts of Papers, and Reports of the Proceedings of the Society, volume XVIII, number 2, London: Printed by George Barclay, Castle Street, Leicester Square and published at the apartments of the [Royal Astronomical] Society, published 1858, page 53

It is generally believed that the planets do not scintillate at all, or scarcely at all. Nevertheless I have often observed a sensible scintillation of Venus and Mars, and in a few rare cases I have also observed a slight scintillation of Jupiter and Saturn. […] I would therefore call the attention of observers who may find themselves under atmospherical conditions of a nature to render the general scintillation very strong, to this point, as they might perhaps be able to ascertain whether Jupiter and Saturn ever sensibly scintillate.

1860 March, Charles Dufour, “XXIX. Instructions for the Better Observation of the Scintillation of the Stars. By Charles Dufour, Professor of Mathematics at Morges.”, in The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, volume XIX (4th Ser.), number CXXVI, London: Taylor and Francis, Red Lion Court, Fleet Street, printers and publishers to the University of London [...], page 223

[…] here and there were Latin inscriptions—obscene scintillations of wit […]

1869, Mark Twain, chapter XXXI, in The Innocents Abroad, page 333