Page:Popular Science Monthly Volume 44.djvu/435

Rh. A pyrometer of platinum, in which was measured the electrical resistance of the metal when exposed to high temperatures, was shown by Mr. Callendar. The display of electrical apparatus also included a very fine high-resistance galvanometer designed by Prof. Oliver Lodge for physiological work; and a magnetic curve-traces contributed by Prof. Ewing. An instrument invented by Mr. John Anderton for projecting solids on a screen attracted much attention. Prof. Boys exhibited photographs of flying bullets, and Dr. Isaac Roberts some admirable photographs, chiefly of nebulæ, showing the probable formation of heavenly bodies. The marked success of the exhibition may lead to like collections being displayed at future meetings of the American Association.

Diversity of Forms and Conditions of Animal Life.—In a paper presented to the Convention of the College Association of the Middle States and Maryland, Dr. Spencer Trotter, speaking of the diversity of life on the earth's surface, remarks upon its correspondence, in a broad way, with the diversity of surroundings. Aquatic animals, like fishes, crayfish, and many insects, inhabit the waters of ponds, lakes, and streams. Frogs and other amphibious creatures are denizens of bays and streams. Some snakes and turtles are aquatic, while others are wholly lovers of the dry land. Birds are found in every situation: ducks and divers on the lakes and rivers; herons and bitterns in marshy fens; gulls and petrels on the open sea; sandpipers along the shores; eagles on lofty mountain peaks; while a host of species enliven the woods and fields. The haunts of mammals are no less diversified. The tree-loving squirrels, the burrowing ground hog, the mole digging out its long subterranean galleries, the water-loving beaver and otter, are each and all associated in the mind with their favorite surroundings. The idea of the animal and its particular home is not new. The story is told in peculiar language in Psalm civ: "The cedars of Lebanon, which he hath planted; where the birds make their nests: as for the stork, the fir trees are her house. The high hills are a refuge for the wild goats; and the rocks for the coniesrabbits [sic]." If this diversity of life is so apparent in a limited area, it is far more so when we come to journey over an extended portion of the earth's surface. As the horizon widens newer and more significant features rise into view. Lofty mountain ranges, broad seas, trackless deserts, treeless plains, and vast forests successively present themselves. Climate and vegetation change from one region to another, and it is not a matter of surprise to find corresponding changes in animal life. Many kinds of animals are limited to particular regions, while others range through wide areas of country under a variety of physical changes. A traveler starting on the Atlantic seaboard of the United States and journeying westward along the fortieth parallel will pass successively through a number of distinct regions, each characterized by certain conditions of climate, vegetation, and peculiar animals. A number of familiar forms will, however, be found throughout the entire extent of the journey across the continent. If the traveler cross the Pacific to Japan, he will find forms of familiar types, though the species are all different from those he knew in America. Should he sail westward by the shortest route to England, he would pass the shores of countries wholly different from those he had left and from each other, each tenanted by strange forms of life—beasts, birds, reptiles, insects, and vegetation—distinct from any he had previously seen. In England, he would be struck by the likeness of the birds to those of Japan, while he would see none of the familiar species of North American birds. We learn from a survey of these conditions how intimately related an animal is to the earth, and how each species is fitted to the special conditions of the region it inhabits.

Crocodiles, Alligators, and the Heloderm.—Crocodiles from the Nile, India, and Ceylon share the tanks at the London Zoölogical Gardens with the alligators from America. The crocodile, says an English writer who has observed them, evidently bears the same analogy to the alligator as the frog to the toad. It is lighter in color and in build, and a more active as well as a more malicious creature. It is not so entirely hideous, though the lower jaw shows projecting tusks like those of a wild boar. The creature's eyes, celebrated in connection with the "crocodile tears"