Page:Popular Science Monthly Volume 49.djvu/143

Rh used by him for chronophotography, as he calls this art, has for its chief peculiarity two circular diaphragms behind the object glass which revolve in opposite directions. There are openings in these disks, and when two of them come opposite the lens there is a momentary exposure of the photographic plate. With suitable accessories, including a specially constructed tank, the same apparatus is used for photographing the movements of aquatic creatures and the motion of waves. When it is desired to take a large number of images per second the apparatus must be modified so as to use a moving film instead of a fixed plate, and for photographing free birds and some other objects whose motion can not be controlled, the photographic gun is employed with the film. In the volume before us the author describes the results he has obtained with these forms of apparatus in recording the movements of man, the horse, birds, fish, starfish, jellyfish, reptiles, the crawling and flying of insects, the squirm of the eel, and the pollywog's wiggle. The methods that have been devised for meeting special difficulties are remarkably ingenious. Thus, when the movements of a running man are to be pictured at such short intervals that the successive images would be partly superposed and hence give a confused picture, the subject is dressed in black with white marks on the head, arm, and leg. The result, which consists of images of these marks only, suggests the march of a file of skeletons at the double quick, and can be very readily studied. After the same manner the trajectory of an insect's wing is sometimes made visible by gilding its tip, or that of a crow's wing by affixing a bit of white paper to the end of one of the feathers. Chronophotography has also been applied to experimental physiology, and M. Marey gives us a series of pictures representing the movements of the heart of a tortoise under artificial circulation. Moreover, movements visible only under the microscope can be pictured by this process, but only a beginning has been made in the latter field. The volume appears in the familiar form of the International Series, and is illustrated with over two hundred figures.

One who would know the birds of Britain can hardly do better than allow himself to be introduced to them by Mr. Hudson This author writes for the general reader and the amateur rather than the ornithologist; hence he gives the coloring and size of each species in from three to six lines, and follows this with a popular description of its feeding and nesting, habits, song, etc. He describes all the species that reside permanently, or for a portion of each year, within the limits of the British Islands, and takes pains to distinguish from these the occasional visitors and the stragglers, to which he gives only brief mention. In his descriptions, especially of song, he frequently quotes John Burroughs, with whom he generally finds himself in agreement. But though the book is untechnical, let no one suppose that it is unscientific. The species are grouped by orders, and follow the arrangement of the British Ornithologists' Union. There is also a chapter on the structure and classification of birds, by Frank E. Beddard. The illustrations of the volume deserve especial mention. There are, first, eight colored plates, from original drawings by A. Thorburn, representing the golden eagle, bearded titmouse, goldfinch, bittern, common teal,