SCIENTIFIC LITERATURE. 131 



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 photo- 

 graphic 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 photo- 

 graphic 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 spe- 

 cial difiiculties 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 imagea 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 sup- 

 pose 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, ptarmi- 



* British Birds. By W. H. Hudson. Pp. 363, crown 8vo. London and New York : Longmans 

 Green & Co. Price, 12s. M., $3.50. 



