Page:Popular Science Monthly Volume 20.djvu/881

Rh The collection of clocks comprises nearly every conceivable variety of time-pieces, from sand-clocks to the Dresden Universal Clock which gave the time at three hundred and sixty places, and automatons driven by clock-work. The collection of telescopes covers nearly the whole history of the instrument, beginning with a Galileo's telescope and including a Kepler's, a Rheita's, the Huygens's, Dolland's, and Frauenhofer's refractors, and several kinds of reflectors. One of the most precious articles in the collection is a very elaborate globe, with all the principal constellations and astronomical lines, and the magnitudes of the stars carefully indicated, which bears an inscription stating that it was made by Mohammed Ben Muwajed-el-Ardhi, without date or place of making. Beigel, of Dresden, calculated in 1808, from the positions of some of the stars on the globe, that it must have been made in the ninth century. Dr. Adolph Drechsler believes that the maker was a son of the famous astronomer Muwajed, who was called by Hulagu, the third emperor of the Mogul dynasty, from Damascus to superintend the observatory at Maragha, and that the date of the instrument was about 1279. The chief value of the collection is in the opportunities it affords for the study of the development of instruments in the several branches of science.

Evolution of Deer-Horns.—Mr. W. Boyd Dawkins has called attention to the confirmation of the doctrine of evolution afforded by the development of the antlers of animals of the deer-kind. In the middle stage of the Miocene, the cervine antler consists merely of a forked crown. This increases in size in the Upper Miocene, though it still remains small and erect, being not quite eleven and a half inches long, with four small tines in Cervus Matheri. The antlers of the succeeding (Pliocene) deer, in the Auvergne, were longer and larger and more branching than those of any earlier deer, and had three or more well-developed tines. The Cervus dicranios of the Upper Pliocene of the Val d'Arno had antlers so complicated as almost to defy description, though they were still smaller than those of the Irish elk. That animal survived into the succeeding age, and has been described in England as Sedgwick's deer. The Irish elk, moose, stag, reindeer, and fallow deer, appeared in Europe in the Pleistocene age, all with highly complicated antlers in the adult, the first having the largest antlers as yet known. "From this survey," says Mr. Dawkins, "it is obvious that the cervine antlers have increased in size and complexity from the mid-Miocene to the Pleistocene age, and that their successive changes have been analogous to those that are observed in the antlers of the living deer, which begin with a simple point and increase in number of tines till their limit of growth is reached. In other words, the development of antlers indicated at successive and widely separated pages of the geological record is the same as that observed in the history of a single living species."

Tests for Color-Blindness.—Dr. William Thomson, of Jefferson Medical College, has devised a test for color-blindness, for use! on the Pennsylvania Railroad, which is in a measure self-working, and may be applied with precision by any agent at any station on the line. It is based on Holmgren's system of many-colored yarns, but the number of skeins is reduced from the one hundred and fifty used by Holmgren to forty. The forty skeins, each bearing its serial number, are hung by buttons, that can be easily unhooked, upon a stick about two feet long, in such a way that the numbers are hid. The first half of the series of yarns, numbered from one to twenty, are devoted to the green test. The odd-numbered skeins are of shades of green, and the even-numbered ones of "confusion colors"—grays, tans, light browns, etc. The other half is similarly occupied with skeins of red, and the "confusion colors" for red-browns, sages, and dark olive, arranged alternately. A man placed before the instrument is told to select ten skeins to match the green test-skein, which is shown him. If his eyes are normal, he will readily select the ten green skeins, and the clerk simply finds the numbers of the skeins thus selected and puts them down. If the man's eyes are defective, he will hesitate in selecting the skeins; if color-blind, he will throw out skeins at