Nature's Teachings: Human Invention Anticipated by Nature

by J. G. Wood

Take, for example, the wonderful tunnels which have been driven through the earth, of which the Mont Cenis Tunnel is one of the greatest triumphs of modern engineering. Beginning, as the workmen did, at opposite ends of a tunnel many miles in length, and labouring only by the lines laid down by the engineers, the men worked steadily on until they met in the centre.

A few blows, and the then narrow dividing wall was shattered, the men shook hands through the aperture, and then, after enlarging it, leaped wildly from one side to the other, having successfully solved the great problem. With such marvellous precision had the lines been laid, that only a few inches had to be smoothed down on either side, and the sides or walls of the tunnel showed no traces of the junction.

So rapid has been the progress of engineering that a tunnel of a mile in length would, within the memory of man, have been thought as daring a project as was the Mont Cenis Tunnel, which has just been given as an example. Indeed, I know of a railway tunnel, not quite a mile in length, where the engineers had committed some error, so that the two halves, instead of meeting exactly, overlapped each other so much that the mistake was only discovered by the workmen, who heard the strokes of their companions’ picks on their sides, and not in front. Consequently, a great waste of time took place, and the centre of the tunnel had to be made with a double curve, like the letter S, and trains are obliged to slacken speed until they have passed it.

Those who have lived long enough to remember the current literature of the past generation will call to mind the ridicule that was cast upon the idea of a tunnel that should pass under the Thames. That it would be useful if it could be completed, no one ventured to doubt, but that such an idea could be conceived by any one out of a lunatic asylum was rather too much for the journalists of the day. However, the tunnel was made, and so proved the theorists wrong on the one side. And, when made, it was of very little use, which proved them wrong on the other side. Now the proposal to carry a submarine tunnel from England to France excites not half the opposition that was elicited by the comparative child’s-play of a tunnel under the Thames.

The only mode of laying down the lines on which the men worked is by suspending very heavy balls to very fine wires, and then, by means of delicate optical instruments, ascertaining whether the wires are in line with each other.

Familiar instances of the use of this principle may be seen in the plumb-rule and level of the builder or carpenter. The latter, with a base of ten feet in length, is often used by the gardener when he wishes to lay the absolutely level lawns that are required for our modern game of croquet, where the hoops are scarcely wider than the balls, and the lawn has in consequence to be nearly as level as a billiard table.

I may here remark that the name plumb-rule is derived from the Latin word plumbum, or lead, in allusion to the leaden weight at the end of the string. The word “plumber” is due to the same source, and signifies a worker in lead.

These invaluable aids to the development of civilisation are due to one principle, namely, that which we call Gravitation, but which ought more properly to be termed Attraction, and which attracts all parts of the earth towards its centre. We are all familiar with the anecdote of Newton and the falling apple, which may be true or not, but which at all events bears on the present subject. No matter on what portion of the spherical earth a tree may be, every fruit becoming disengaged from it is attracted to the earth, the line which it takes, unless disturbed by external forces (such as wind, &c.), being that which passes from the zenith to the centre of the earth.

This imaginary line is a perfect perpendicular, and the visible line which is formed by the delicate wire of the tunnel-boring engineering instrument, or the comparatively coarse string of the plumb-rule and level, are approximations sufficiently close for practical purposes. So it is in a mathematical proposition. As mathematical lines have no breadth, they are simply indicated or represented by the lines of the figure, the bodily eye being incapable of seeing what is perfectly visible to the mental eye, namely, length without width. So the wire and string perform in practical work exactly the same office which is fulfilled by the lines of a mathematical proposition drawn on paper.