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NOTE 1. p. 7.

THE HOROLOGE OF FLORA is alluded to by Pliny with his usual felicity of thought and expression. “ Dedi tibi herbas horarum indices; et ut ne sole quidem oculos tuos a terra avoces, heliotropium ac lupinum circumaguntur cum illo. Cur etiam altius spectas, ipsumque cælum scrutatis ? Habes ante pedes tuos ecce Vergilias.”—Hist, Nat. lib. xviii. c. 27.

Linnæus enumerates forty-six flowers which possess this kind of sensibility. The following are a few of them, with their respective hours of rising and setting, as the Swedish naturalist terms them. He divides them into meteoric flowers, which less accurately observe the hour of unfolding, but are expanded sooner or later, according to the cloudiness, moisture, or pressure of the atmosphere.

2d. Tropical flowers, which open in the morning, and close before evening every day; but the hour of the expanding becomes earlier or later, as the length of the day increases or decreases.

3d. Equinoctial flowers, which serve for the construction of Flora's dial, since they open at a certain and exact hour of the day, and for the most part close at another determinate hour: for instance, the Leontodon Taraxacum, dandelion, opens at 5–6, closes at 8–9; Hieracium Pilosella, mouse-ear hawkweed, opens at 8, closes at 2; Tragopogon pratensis, yellow goat’s-beard, opens at sunrise, and shuts at noon with such regularity, that the husbandman who adopts it as the signal of dinner-time need not fear to have his pudding too much or too little boiled; Sonchus lævis, smooth sow-thistle, opens at 5, closes at 11-12; Lactuca sativa, cultivated lettuce, opens at 7, closes at 10; Tragopogon luteum, yellow goat's-beard, opens at 3–5, closes at 9-10; Lapsana, nipplewort, opens at 5–6, closes at 10-11; Nymphæa alba, white water-lily, opens at 7, closes at 5; Papaver nudicaule, naked poppy, opens at 5, closes at 7; Hemerocallis fulva, tawny day-lily, opens at 5,closes at 7–8; Convolvulus, opens at 5–6; Malva, mallow, opens at 9-10, closes at 1; Arenuria purpurea, purple sandwort, opens at 9-10, closes at 2–3; Anagallis, pimpernel, opens at 7–8; Portulaca hortensis, garden purslain, opens at 9-10, closes at 11-12; Dianthus prolifer, proliferous pink, opens at 8, closes at 1; Cichoreum, succory, opens at 4-5; Hypocharis, opens at 6-7, closes at 4-5; Crepis, opens at 4-5, closes at 10-11; Picris, opens at 4-5, closes at 12; Calendula Africana, opens at 7, closes at 3-4, &c.

“ Thus in each flower and simple bell,

That in our path betrodden lie,
Are sweet remembrancers who tell

How fast the winged moments fly.”

NOTE 2. p. 68.

It may, perhaps, be asked, how this decrease of weight could have been ascertained; since, if the body under examination decreased in weight, the weight which was opposed to it in the opposite scale must also have diminished in the same proportion; for instance, that if the lump of lead lost two pounds, the body which served to balance it must also have lost the same weight, and therefore that the different force of gravity could not be detected by such means. It is undoubtedly true that the experiment in question could not have been performed with an ordinary pair of scales, but by using a spiral spring it was easy to compare the force of the lead's gravity at the surface of the earth, and at four miles high, by the relative degree of compression which it sustained in those different situations. We may take this opportunity of observing, that as the force of gravity varies directly as the mass, or quantity of matter, a body weighing a pound on our earth would, if transferred to the sun, weigh 27} pounds; if to Jupiter, 34 lbs.; if to Saturn, 14; but, if to the moon, not more than three ounces.

NOTE 3. p. 74.

In order to perform this experiment with the highest degree of accuracy, a body of considerable specific gravity should be selected, such as lead or iron; for a common stone experiences a considerable retardation in falling, from the action of the air. Where the arrival of the body at the bottom of the cavern to be measured cannot be seen,

we must make allowance in our calculation for the known velocity of sound; thus, suppose a body were ascertained to fall in five seconds. As a heavy body near the earth's surface falls about 167 feet in one second of time, or for this

purpose 16 feet will be sufficiently exact; and as sound travels at the rate of 1142 feet per second, multiply together 1142, 16 and 5, which will give 91360, and to four times this product, or 365440, add the square

of 1142, which is 1304164, and the sum will be 1669604; then if from the square root of the last number = 1292 the number 1142 be subtracted, the remainder 150 divided by 32 will give 4•69 for the number of seconds which elapsed during the fall of the body; if this remainder be subtracted from 5, the number of seconds during which the body was falling and the sound returning, we shall have 0.31 for the time which the sound alone employed before it reached the ear; and this number multiplied by 1142, will give for product 354 feet, equal the depth of the well. This rule, which, it must be allowed, is rather complex, is founded on the property of falling bodies, which are accelerated in the ratio of the times, so that the spaces passed over increase in the square of the times.

The following is a more simple but less accurate rule. Multiply 1142 by 5, which gives 5710; then multiply also 16 by 5, which gives 80, to which add 1142, this gives 1222, by which sum divide the first product 5710, and the quotient 4:68 will be the time of descent, nearly the same as before. This taken from 5, leaves 0.32 for the time of the ascent; which, multiplied by 1142, gives 365 for the depth, differing but little from the former more exact number.

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