Open main menu

Page:Popular Science Monthly Volume 19.djvu/289

This page has been proofread, but needs to be validated.

rangements made for systematic work in the laboratory, and a part of the class will be allowed to join each day in the dredging and collecting expeditions. Dr. Brooks will exercise personal supervision of the work of this class, and will give a course of lectures on general zoölogy, but the students will be under the more immediate guidance of Dr. S. F. Clarke, who will lecture daily on the structure and habits of marine animals. Beaufort, on account of its diversified fauna, and of its mild and uniform climate, is described as a desirable place for study during the hot months of summer.


Trees and Lightning.—Professor Colladon, of Geneva, published the conclusion several years ago that, when lightning strikes a tree, it is received on the ends of the branches, which, being excellent conductors, lead it, without suffering disturbance, down to the larger limbs. Thence it descends to the main limbs and the trunk, whose conducting power, intrinsically inferior to that of the smaller and younger shoots of the top, is insufficient to sustain the concentrated force of the currents which have united here from the thousand channels by which they have so far descended. Here, then, generally appear the first marks of the shock, not because the lightning has struck the tree at that place, as might be superficially supposed, but because the conducting powers of the tree begin to fail at this point-This view was satisfactorily confirmed by the effect of the lightning upon a poplar-tree, which was struck at Geneva on the 5th of May, 1880. The young, tender leaves of the main topmost branch of this tree and of the branches immediately below it were torn up into small fragments, which strewed the ground below them, as if they had undergone a violent shock of air, such as would be produced by an explosion of dynamite. Many trees may be compared, in respect to their power to conduct electricity, to structures of wood or masonry, which are well furnished with conductors on their upper part, but with which no conducting connection with the ground is given. If such a building were struck with lightning, its upper part would not be hurt, while its lower part would suffer badly. The danger of being struck by lightning, to which persons standing under a tree are exposed, is thus accounted for. The top of the tree, bristling with conducting twigs, attracts the lightning; the current, meeting with non-conducting obstacles at the trunk, jumps from it to the surrounding bodies, whether they be bushes or men and animals. Of two persons, one standing under the tree, the other sitting among the limbs at the top, the latter would be in a vastly safer position. Birds having nests in trees are rarely struck by lightning, and their nests are hardly ever damaged. Large trees growing near a house will protect it from lightning, provided there is no pond or well or stream beyond the house to attract the current across it. If the water is on the same side of the house as the tree, or the tree is between it and the house, or has a rod attached to it, the protection is almost perfect. When a vineyard is struck by lightning, the leaves over a large circuit will, a few hours or days afterward, appear discolored, showing that the electrical action has taken place in a diffused manner, and not in a concentrated attack. In such cases hundreds or even thousands of vines may be affected, showing palpably that it is the property of lightning to manifest itself upon the whole top of a tree or a plot of vegetation. In his memoir on this subject, M. Colladon mentions a single stroke of lightning which left its traces on more than two thousand things.


Progress of Cremation.—Cremation is growing in favor throughout Europe. The first furnace for the purpose was erected at Milan, in 1875; the second, built at Gotha, in 1878, has been recognized by the authorities of the city, so that there the choice between burial and cremation is free to every citizen. Several societies for the advancement of the rite have been formed, some of them even in states where no preparations have been made for performing it. The International Hygienic Congress which met at Milan in September, 1880, adopted a resolution in favor of compelling the bodies of all animals dying of contagious diseases to be incinerated, and of the provision of facilities for that purpose in every parish. It also appointed a special international