CHAPTER XXXIV. THE AUTHOR’S FURTHER CONTRIBUTIONS TO HUMAN KNOWLEDGE.
Glaciers — Uniform Postage — Weight of the Bristol Bags — Parcel Post — Plan for transmitting Letters along Aërial Wires — Cost of Verification is part of Price — Sir Rowland Hill — Submarine Navigation — Difference Engine — Analytical Engine — Cause of Magnetic and Electric Rotations — Mechanical Notation — Occulting Lights — Semi-occultation may determine Distances — Distinction of Lighthouses numerically — Application from the United States — Proposed Voyage — Loss of the Ship and Mr. Reid — Congress of Naval Officers at Brussels in 1853 — My Portable Occulting Light exhibited — Night Signals — Sun Signals — Solar Occulting Lights — Afterwards used at Sebastopol — Numerical Signals applicable to all Dictionaries — Zenith Light Signals — Telegraph for Ships on Shore — Greenwich Time Signals — Theory of Isothermal Surfaces to account for the Geological Facts of the successive Uprising and Depression of various parts of the Earth’s Surface — Games of Skill — Tit-tat-to — Exhibitions — Problem of the Three Magnetic Bodies.
Of Glaciers.
MUCH has been written upon the subject of glaciers. The view which I took of the question on my first acquaintance with them still seems to me to afford a sufficient explanation of the phenomena. It is probable that I may have been anticipated in it by Saussure and others; but, having no time to inquire into its history, I shall give a very brief statement of those views.
The greater part of the material which ultimately constitutes a glacier arises from the rain falling and the snow deposited in the higher portions of mountain ranges, which {442} naturally first fill up the ravines and valleys, and rests on the tops of the mountains, covering them to various depths.
The chief facts to be explained are—first, the causes of the descent of these glaciers into the plains; second, the causes of the transformation of the opaque consolidated snow at the sources of the glacier into pure transparent ice at its termination.
The glaciers usually lying in valleys having a steep descent, gravity must obviously have a powerful influence; but its action is considerably increased by another cause.
The heat of the earth and that derived from the friction of the glacier and its broken fragments against the rock on which it rests, as well as from the friction of its own fragments, slowly melts the ice, and thus diminishing the amount of its support, the ice above cracks and falls down upon the earth, again to be melted and again to be broken.
But as the ice is upon an inclined plane, the pressure from above, on the upper side of the fragment, will be greater than that on the lower; consequently, at every fall the fallen mass will descend by a very small quantity further into the valley. Another consequence of the melting of the lower part of the centre of the glacier will be that the centre will advance faster than the sides, and its termination will form a curve convex towards the valley.
The above was, I believe, the common explanation of the formation of glaciers. The following part explains my own views:—