[2.] “Mayonnaise,” māˈyon-naise.
THE CIRCLE OF THE SCIENCES.
[1.] “Tufa.” A kind of volcanic sandstone, composed of pulverized volcanic rocks. It is formed whenever a shower of rain accompanies the fall of cinders, during the eruption of a volcano.
[2.] “Drift period.” The name applied to the time in which that remarkable bed of earth, gravel, and stones of all dimensions, was deposited. It has puzzled all geologists to account for this formation, which is the lowest of the three groups of the superficial covering of the earth, and no completely satisfactory theory has yet been advanced.
[3.] The large New Zealand bird described was called the moa.
[4.] “Carboniferous period.” Coal age. By careful study it has been found that in the progress of the earth’s development a number of great ages have existed—each distinguished from the others by some marked change. That of coal plants is placed by geologists as the fourth age, counting upward from the lowest formation. It was remarkable for the alternate low elevation of the land above the sea level, and its submergences; and also for the luxuriant growth of vegetation, which, under the great pressure and heat to which it was subjected while the surface was submerged, was changed into coal.
[5.] “Spectroscope.” The name given to the apparatus used for the study of the spectrum. “When a ray of sunlight admitted through an aperture in a dark room is concentrated upon a prism of rock salt”—or glass—“by means of a lens of the same material, and then after emerging from the prism is received on a screen, it will be found to present a band of colors, in the following order: red, orange, yellow, green, blue, indigo, and violet.”—Ganot. This band is called the spectrum. That there are other but invisible lines than those mentioned in the spectrum, is proven by the use of the thermopile, oftener called thermomultiplier, mentioned in the article on “Home Studies in Chemistry.” This is a complicated instrument used for detecting minute differences in the degrees of heat; its description without an accompanying illustration would be of no benefit to any one. So delicate is it that the heat of the hand held at a distance of three feet is sufficient to deflect the needle. The spectroscope is composed of three telescopes, mounted on a common foot, whose axes converge toward a glass prism. One of the telescopes is movable, and can be adjusted so as to give the observer the clearest view of the spectrum. The ray of light is admitted through the telescope and falls upon the prism, which decomposes it, and the spectrum is formed on the opposite side of the prism. In the telescope which the observer uses a powerful magnifying glass is placed. The third telescope is used for measuring the relative distances between the lines.