the ethereal waves of still more rapid undulations and lesser length furnish the actinic force of light. And if the mathematical deductions of such as Maxwell and Boltzmann, together with the refined researches of many others in this border-land of science, are not at fault, we would not be surprised if, at some early day, the solution of the phenomena of electricity should be found in some way connected with ethereal vibrations, infinitely more rapid and minute than those which produce the actinism of the ultra-violet spectrum. The difficulties attending the solution of this problem may be more fully comprehended when we recollect that, in dealing with vibrations more rapid than those bordering the visible spectrum, we are leaving regions where the undulations comprise nearly one thousand million of millions in a second of time, only to be confronted with others of infinitely greater rapidity.
These ethereal and molecular actions are going on eternally about us. The photographer's sensitized plate may receive an image that maps out the constellations, or, through the prism of the spectroscope in lines of light, we may read of the constituents of the nebulae, and thus upon the waves of ether do we hold communion across the universe by that ethereal chain of motion which binds us to the stars!
| SIMPLE EXPERIMENTS IN OPTICS. |
By ELIZA A. YOUMANS.
THE little work of Mayer and Barnard, designed to introduce beginners to the experimental study of optics, is so much needed, so skillfully done, and may be so helpful to teachers and students of all ages, that it is desirable to offer a few illustrations of the method of experiment adopted, and to point out some of the cheap and simple ways which Prof. Mayer has hit upon for exemplifying and proving optical phenomena. We shall make free use of his text as well as his cuts in the present article. Fig. 1, for example, represents the arrangement adopted to prove that light moves in straight lines. He first gets three little blocks, two or three inches square; then three slips of pine, three inches by four and one-eighth of an inch thick; and then three postal-cards, through which a small aperture is to be made. The authors say: "Just here we need a tool for making small holes and doing other work in these experiments; and we push, with a pair of pliers, a cambric needle into the end of a wooden pen-holder or other slender stick, putting the eye-end into the wood, and thus making a needle-pointed awl." This is an excellent little contrivance, and we suggest to the pupil to make a set of them with different-sized needles, which he will find very useful. Now, lay the postal-
