Page:Popular Science Monthly Volume 17.djvu/806

In his "Method for making a History of the Weather,"^[1] the attention of observers is especially directed to the following "particulars," as "requisite for the raising of axioms whereby the cause or laws of weather may be found out": 1. The strength and quarter of the winds. 2. The degrees of heat and cold. 3. The degrees of dryness and moisture observed with a hygroscope "made with the single beard of a wild oat perfectly ripe, set upright and headed with an index." 4. The degrees of pressure of the air. 5. The constitution and face of the sky.

It is perhaps worth remarking that our present system of meteorological observations corresponds with tolerable accuracy to Bacon's notion of how a "history" of any special branch of physics should be compiled; with this difference in result, that, instead of arriving at "axioms" and "forms," we have as yet obtained only a set of empirical rules which, however practically useful, can scarcely be said to constitute a science.

"Discoursed with Mr. Hooke," Pepys wrote, August 8, 1666, "about the nature of sounds, and he did make me understand the nature of musicall sounds made by strings, mighty prettily; and told me that having come to a certain number of vibrations proper to make any tone, he is able to tell how many strokes a fly makes with her wings (those flies that hum in their flying) by the note that it answers to in musique, during their flying. That, I suppose, is a little too much refined, but his discourse in general of sound was mighty fine."^[2]

Notwithstanding Mr. Pepys's skepticism, Hooke was on this occasion not "refining" overmuch. He exhibited in 1681 an instrument (with the principle of which he had doubtless long been acquainted) for counting the pulsations of sound, which seems to have been virtually identical with that now known as "Savart's Wheel." He also anticipated Chladni's celebrated experiment by strewing flour on a vibrating glass bell, thus presenting to the eye, as it were, a picture of the configuration of rest and motion on its surface. It was one of his favorite ideas that, by some future discovery, the sense of hearing would be reënforced as prodigiously as the sense of sight had already been by the telescope—an intuition singularly realized by the recent invention of the telephone. "It has not yet been thoroughly examined," he wrote in 1664,^[3] "how far Otocousticons may be improved, nor what other ways there may be of quickening our hearing, or conveying sound through other bodies than the air." "By very casual trials," he tells us elsewhere, he had made some progress in this direction, and was by no means convinced that they might not be prosecuted so far as to render audible noises made at the distance of the planets! Although acknowledging that to his own prejudices this seemed "a very extravagant conjecture, . . . yet methinks," he adds, "I should have

1. Published by Sprat, "History of the Royal Society," p. 173.
2. Pepys's "Diary," vol. iv., p. 43, Bright's edition.
3. "Micrographia," preface.