Democratic Sentinel, Volume 17, Number 5, Rensselaer, Jasper County, 17 February 1893 — POPULAR SCIENCE NOTES. [ARTICLE]

POPULAR SCIENCE NOTES.

Trees Struck by Lightning. —Mr. D. lonesco has compiled statistics concerning trees which are struck by lightning, md arrives at the following interestmg conclusions, which are given in the last issue of the Electrical World: It lias beeu supposed for a long time that certain kinds of trees are particularly subject to destruction by lightning, while others are quite free from danger. Among the first is the oak and among the latter the laurel. An investigation of this statement led the writer to the following conclusions: “At very high potential electrical discharges ail kinds of trees may be subject to destruction from lightning. Trees containing oils are less subject to be struck; those containing very much oil being protected the most. Lightning appears to prefer those trees which contain oil to a slight decree only in 3ummer. The quantity of" water contained in the trees has no effect on their liability to being struck. Dead limbs of trees, of those containing starch as well as of those containing oil, are particularly subject to being struck. Cambium, bark and leaves do not alter the conductivity of trees. The nature of the soil has noconnection with the frequency of the destruction of the trees by lightning.”

Foundations for Sea Walls.—Successful methods in securing suitable foundations for sea walls are amoug the most important of modern engineering triumphs, and one of the latest of these is what has come to be known as the Shield system, originated abroad, and of special adaptation where the bottom is of irregular rocky service. Careful longitudinal sections are taken along thelines of the inner and outer facSs of the foundations, and planks cut and nailed to timbers in such a manner that one edge of the finished frame conforms exactly with the rocky bottom; theseframes are weighted and sunk intoplace, where they are fastened by long bolts wedged into the rock in such a manner that a mould for about twenty feet of the bottom of the wall is thus formed. The tops of the frames are brought to a true horizontal position by means of a spirit level, and the space between is tilled with concrete; where a large mass of the latter is used, it is composed of four to four and one-half parts of sand and gravel to one of Portland cement, the top being finished off with concrete composed of one and a half totwo parts of sand and gravel to one of cement. The material is lowered in a. canvas bag holding about two and onefourth cubic feet, and so arranged that the bottom can be easily opened when it touches the spot where the concrete is tobe laid. The material as it leaves the bag is simply pressed down by the flat hand to the required level, and then gently struck off by a straight edge resting at each edge on the frames. In this way a perfect surface is formed five or six feet below water, becoming hard enough in three days to receive the blocks of the wall. Velocity of Rain Drops. —Of course we all know that it would be an utter impossibility for storm clouds to form and rain to fall were it not for the forty odd miles of atmosphere that rises above our heads; but, supposing it were possifor human beings to exist in an atmosphere that only rose to a level with their mouths, and that storm clouds could form in the region outside such a low-grade atmosphere, then every rain drop would prove as fatal to earthly creatures as if it were a steel bullet fired from a dynamite gun. All falling bodies, whether they be crystal rain drops or meteorites, fall with what philosophers term “a uniform accelerated motion;” in other words, if a body be moving at a certain velocity at the expiration of one second from the beginning of its fall, it will be moving with twice that velocity at the expiration of two seconds, gaining in speed at a uniform rate throughout the course of its fall. Careful experiments have shown that the rate per second at which bodies acquire velocity in falling through the air is thirty-two feet per second at the end of the first second from starting. At the end of the next second it is going at the rate of sixtyfour feet per second, and so on through the whole time of falling. Where the velocity is known the space through which the body has fallen may be ascertained by multiplying the velocity at that period by the number of seconds during which it has been falling, and dividing the result by two. This rule applies, however, only to bodies falling through a vacuum. The resistance of our atmosphere materially retards rain drops, hailstones, aerolites and all other bodies which fall through it, and were it not for the resistance it presents, every rain storm would be disastrous to the human race, as each drop would fall with a velocity great enough to penetrate the full length of a full-grown man’s body. —[Nature. .