The ascent of Mont Blanc from the Valley of Chamouni is considered, and with justice, as the most toilsome feat that a strong man can execute in two days.  The combustion of two pounds of coal would place him on the summit.

The Wonders of Physics.

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.

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