The lower end of the rod should enter the earth so deep as to come at the moist part, perhaps two or three feet; and if bent when under the surface, so as to go in a horizontal line six or eight feet from the wall, and then bent again downwards three or four feet, it will prevent damage to any of the stones of the foundation.
A person apprehensive of danger from lightning, happening during the time of thunder to be in a house not so secured, will do well to avoid sitting near the chimney, near a looking-glass, or any gilt pictures or wainscot; the safest place is in the middle of the room, (so it be not under a metal lustre suspended by a chain,) sitting in one chair and laying the feet up in another. It is still safer to bring two or three mattresses or beds into the middle of the room, and, folding them up double, place the chair upon them; for they, not being so good conductors as the walls, the lightning will not choose an interrupted course through the air of the room and the bedding, when it can go through a continued better conductor, the wall. But where it can be had, a hammock or swinging-bed, suspended by silk cords equally distant from the walls on every side, and from the ceiling and floor above and below, affords the safest situation a person can have in any room whatever; and what, indeed, may be deemed quite free from danger of any stroke by lightning.
The Leech, a Prognosticator of the Weather.
Confine a leech in a large phial, three parts filled with rain water, regularly changed twice a week, and placed on a window frame, fronting the north. In fair and frosty weather it lies motionless, and rolled up in a spiral form, at the bottom of the glass: but prior to rain or snow, it creeps up to the top, where if the rain will be heavy and of some continuance, it remains a considerable time; if trifling, it quickly descends. Should the rain or snow be accompanied with wind, it darts about its habitation with amazing celerity, and seldom ceases until it begins to blow hard. If a storm of thunder or lightning be approaching, it is exceedingly agitated, and expresses its feelings in violent convulsive starts, at the top of the glass. It is remarkable that however fine and serene the weather may be, and not the least indication to change, either from the sky, the barometer, or any other cause whatsoever, yet, if the animal ever shift its position, or move in a desultory manner, so certain will the coincident results occur, within thirty-six hours, frequently within twenty-four, and sometimes in twelve; though its motions chiefly depend on the fall and duration of the wet, and the strength of the wind.
The Awn of Barley an Hydrometer.
The awn of barley is furnished with stiff points, which, like the teeth of a saw, are all turned towards the point of it; as this long awn lies upon the ground, it extends itself in the moist air of night, and pushes forward the barley-corn, which it adheres to in the day; it shortens as it dries; and, as these points prevent it from receding, it draws up its pointed end, and thus, creeping like a worm, will travel many feet from the parent stem. That very ingenious mechanic philosopher, Mr. Edgworth, once made on this principle a wooden automaton: its back consisted of soft fir-wood, about an inch square, and four feet long, made of pieces cut the cross-way in respect to the fibres of the wood, and glued together; it had two feet before, and two behind, which supported the back horizontally, but were placed with their extremities, which were armed with sharp points of iron, bending backwards. Hence, in moist weather, the back lengthened, and the two foremost feet were pushed forwards; in dry weather the hinder feet were drawn after, as the obliquity of the points of the feet prevented it from receding.
The Power of Water when reduced to Vapour by Heat.
Whatever force water may have while its parts remain together, is nothing, if compared to the almost incredible power with which its parts are endued, when they are reduced to vapour by heat. Those steams which we see rising from the surface of boiling water, and which to us appear feeble, yet, if properly conducted, acquire immense force. In the same manner as gunpowder has but small effect, if suffered to expand at large, so the steam issuing from water is impotent, where it is permitted to evaporate into the air; but where confined in a narrow compass, as, for instance, where it rises in an iron tube shut up on every side, it there exerts all the wonders of its strength. Muschenbrook has proved by experiment, that the force of gunpowder is feeble when compared to that of rising steam. A hundred and forty pounds of gunpowder blew up a weight of thirty thousand pounds: but, on the other hand, a hundred and forty pounds of water, converted by heat into steam, lifted a weight of seventy-seven thousand pounds; and would lift a much greater, if there were means of giving the steam more heat with safety; for the hotter the steam the greater is its force.
Artificial Memory.
In travelling along a road, the sight of the more remarkable scenes we meet with, frequently puts us in mind of the subjects we were thinking or talking of when we last saw them. Such facts, which were perfectly familiar, even to the vulgar, might very naturally suggest the possibility of assisting the memory, by establishing a connexion between the ideas we wish to remember, and certain sensible objects, which have been found from experience to make a permanent impression on the mind. It was said, that a person contrived a method of committing to memory the sermons which he was accustomed to hear, by fixing his attention, during the different heads of the discourse, on different compartments of the roof of the church, in such a manner as, that when he afterwards saw the roof, or remembered the order in which its compartments were disposed, he recollected the method which the preacher had observed in treating his subject. This contrivance was perfectly analogous to the topical memory of the ancients; an art which, whatever be the opinion we entertain of its use, is certainly entitled, in a high degree, to the praise of ingenuity.