THE ESSAYS AS STATEMENTS OF SCIENTIFIC RESULTS
The first reading of either essay will disclose some of the most marvelous results that have been reached by scientific investigation. For example, it has been discovered that light is of an undulatory nature; that the vibrations of light quiver at the rate of several hundred million of million times a second; that light is transmitted over interplanetary distances with a velocity of nearly 200,000 miles a second; and that for the transmission at such a speed through what seems to us to be empty space, as between the sun and the earth, there must be a continuous, extremely tenuous, and highly elastic medium, all pervading and universally extended, to which the name, luminiferous ether, is commonly given. It is of course not to be expected that all these and many other results, physical, geometrical, and numerical, can be easily acquired; some paragraphs must be gone over more slowly than others, and many of them should be reviewed more than once; some are difficult of comprehension because they are without the vivid experiments by which they were illustrated in the original lecture; and others because they are compressed into terse statements without explanation. But at the end of what is here called the “first reading,” many of the conclusions announced regarding the nature of light should be fairly familiar. Similar examples may be drawn from the lecture on the tides; the larger share of mathematical considerations here encountered may make the second essay more difficult than the first; if some readers do not clearly understand, for example, the statement regarding diurnal inequality (p. 291), they may be excused, for the statement is very brief; similarly, the account of the tide machines (pp. 293-297) is too dense to be really comprehended by a non-mathematical reader, previously uninformed on such matters as harmonic analysis.