What mere assertion will make any man believe that in one second of time, in one beat of the pendulum of a clock, a ray of light travels over 192,000 miles, and would therefore perform the tour of the world in about the same time that it requires to wink with our eyelids, and in much less than a swift runner occupies in taking a single stride? What mortal can be made to believe, without demonstration, that the sun is almost a million times larger than the earth? and that, although so remote from us, that a cannon ball shot directly towards it, and maintaining its full speed, would be twenty years in reaching it, it yet affects the earth by its attraction in an inappreciable instant of time?—Who would not ask for demonstration, when told that a gnat's wing, in its ordinary flight, beats many hundred times in a second? or that there exist animated and regularly organised beings, many thousands of whose bodies laid close together would not extend an inch? But what are these to the astonishing truths which modern optical inquiries have disclosed, which teach us that every point of a medium through which a ray of light passes is affected with a succession of periodical movements, regularly recurring at equal intervals, no less than 500 millions of millions of times in a single second! that it is by such movements, communicated to the nerves of our eyes, that we see—nay more, that it is the difference in the frequency of their recurrence which affects us with the sense of the diversity of colour; that, for instance, in acquiring the sensation of redness our eyes are affected 482 millions of millions of times; of yellowness, 542 millions of millions of times; and of violet, 707 millions of millions of times per second. Do not such things sound more like the ravings of madmen, than the sober conclusions of people in their waking senses? They are, nevertheless, conclusions to which any one may most certainly arrive, who will only be at the trouble of examining the chain of reasoning by which they have been obtained.
Extraordinary Property of Shadows.
An eminent living geometer had proved by calculations, founded on strict optical principles, that in the centre of the shadow of a small circular plate of metal, exposed in a dark room to a beam of light emanating from a very small brilliant point, there ought to be no darkness,—in fact, no shadow at that place; but, on the contrary, a degree of illumination precisely as bright as if the metal plate were away. Strange and even impossible as this conclusion may seem, it has been put to the trial, and found perfectly correct.
THE NATURALIST.
RAINING TREES.
(By John Murray, Esq. F.S.A. &c.)
The secretions of trees form a curious part of their physiology, but the influence of vegetation on the atmosphere seems to have been entirely overlooked, at least as far as it regards its meteorology.
In the case of that curious genus of plants the Sarracènia, in which the S. adúnca is most conspicuous, the foliaceous pouch is a mere reservoir, or cistern, to catch and retain the falling dew or rain. In the Nepénthes distillatòria, or pitcher plant, the case is different; and analysis proves it to be an evident secretion from the plant itself, independent altogether of the fact that it is found in the pitcher before the lid has yet opened. I may here state, en passant, that the results, I obtained from a chemical examination of this liquid differ materially from those of Dr. Edward Turner. The Córnus máscula is very remarkable for the amount of fluid matter which evolves from its leaves, and the willow and poplar, when grouped more especially, exhibit the phenomenon in the form of a gentle shower. Prince Maximilian, in his Travels in the Brazils, informs us that the natives in these districts are well acquainted with the peculiar property of those hollow leaves that act as recipients of the condensed vapours of the atmosphere; and, doubtless, these are sources where many tropical animals, as well as the wandering savage, sate their thirst "in a weary land." The Tillándsia exhibits a watery feature of a different complexion: here the entire interior is charged with such a supply of liquid, that, when cut, it affords a copious and refreshing beverage to man. That these extraordinary sources of "living springs of water" are not unknown to inferior creation, is a fact interestingly confirmed to us in the happy incidents detailed by Mr. Campbell, in his Travels in South Africa, where a species of mouse is described to us, as storing up supplies of water contained in the berries of particular plants; and, in Ceylon, animals of the Símia tribe are said to be well acquainted with the Nepénthes distillatòria, and to have frequent recourse to its pitcher. The mechanism of the "rose of Jericho" (Anastática hierochuntìna] shows the susceptibility of plants to moisture in a very remarkable manner; and I have submitted some experiments made with this extraordinary exotic, the inhabitant of an arid sandy soil, to the Horticultural Society of London. That succulents should be found clothing in patches the surface of the burning desert is a phenomenon not the least wonderful in the geographical history of vegetation.