Curiosities of Science, Past and Present / A Book for Old and Young

by John Timbs

As the form of the Earth exerts a powerful influence on the motion of other cosmical bodies, and especially on that of its neighbouring satellite, a more perfect knowledge of the motion of the latter will enable us reciprocally to draw an inference regarding the figure of the earth. Thus, as Laplace ably remarks: “an astronomer, without leaving his observatory, may, by a comparison of lunar theory with true observations, not only be enabled to determine the form and size of the earth, but also its distance from the sun and moon; results that otherwise could only be arrived at by long and arduous expeditions to the most remote parts of both hemispheres.” The compression which may be inferred from lunar inequalities affords an advantage not yielded by individual measurements of degrees or experiments with the pendulum, since it gives a mean amount which is referable to the whole planet.—Humboldt’s Cosmos, vol. i.

The distance of the moon from the earth is about 240,000 miles; and if a railway-carriage were to travel at the rate of 1000 miles a-day, it would be eight months in reaching the moon. But that is nothing compared with the length of time it would occupy a locomotive to reach the sun from the earth: if travelling at the rate of 1000 miles a-day, it would require 260 years to reach it.

CAUSE OF ECLIPSES.

As the Moon is at a very moderate distance from us (astronomically speaking), and is in fact our nearest neighbour, while the sun and stars are in comparison immensely beyond it, it must of necessity happen that at one time or other it must pass over, and occult or eclipse, every star or planet within its zone, and, as seen from the surface of the earth, even somewhat beyond it. Nor is the sun itself exempt from being thus hidden whenever any part of the moon’s disc, in this her tortuous course, comes to overlap any part of the space occupied in the heavens by that luminary. On these occasions is exhibited the most striking and impressive of all the occasional phenomena of astronomy, an Eclipse of the Sun, in which a greater or less portion, or even in some conjunctures the whole of its disc, is obscured, and, as it were, obliterated, by the superposition of that of the moon, which appears upon it as a circularly-terminated black spot, producing a temporary diminution of daylight, or even nocturnal darkness, so that the stars appear as if at midnight.—Sir John Herschel’s Outlines.

VAST NUMBERS IN THE UNIVERSE.

The number of telescopic stars in the Milky Way uninterrupted by any nebulæ is estimated at 18,000,000. To compare this number with something analogous, Humboldt calls attention to the fact, that there are not in the whole heavens more than about 8000 stars, between the first and the sixth magnitudes, visible to the naked eye. The barren astonishment excited by numbers and dimensions in space when not considered with reference to applications engaging the mental and perceptive powers of man, is awakened in both extremes of the universe—in the celestial bodies as in the minutest animalcules. A cubic inch of the polishing slate of Bilin contains, according to Ehrenberg, 40,000 millions of the siliceous shells of Galionellæ.

FOR WHAT PURPOSE WERE THE STARS CREATED?

Surely not (says Sir John Herschel) to illuminate our nights, which an additional moon of the thousandth part of the size of our own would do much better; nor to sparkle as a pageant void of meaning and reality, and bewilder us among vain conjectures. Useful, it is true, they are to man as points of exact and permanent reference; but he must have studied astronomy to little purpose, who can suppose man to be the only object of his Creator’s care, or who does not see in the vast and wonderful apparatus around us provision for other races of animated beings. The planets derive their light from the sun; but that cannot be the case with the stars. These doubtless, then, are themselves suns; and may perhaps, each in its sphere, be the presiding centre round which other planets, or bodies of which we can form no conception from any analogy offered by our own system, are circulating.[19]

NUMBER OF STARS.

Various estimates have been hazarded on the Number of Stars throughout the whole heavens visible to us by the aid of our colossal telescopes. Struve assumes for Herschel’s 20-feet reflector, that a magnifying power of 180 would give 5,800,000 for the number of stars lying within the zones extending 30° on either side of the equator, and 20,374,000 for the whole heavens. Sir William Herschel conjectured that 18,000,000 of stars in the Milky Way might be seen by his still more powerful 40-feet reflecting telescope.—Humboldt’s Cosmos, vol. iii.