the lecture-room, and a great fact in astronomy, are explained on the same principles.

If there were but two bodies in the system, their mutual orbits would be undisturbed. Some conic section would be exactly and forever described by each about their common centre of gravity. But the introduction of a third body disturbs both these orbits, and its own is disturbed by them. In the solar system, therefore, in which hundreds of bodies are attracting each other, the disturbances are almost numberless; though multitudes of them are too minute to be perceived. The two which have now been noticed-namely, the retrogradation of nodes, and the advance of apsides-are among the most prominent. And though in some instances they are exceedingly minute, they at length become apparent, because they go on accumulating for ages instead of oscillating back and forth. The equinoxes, though they have an oscillatory inequality in their motion, are yet perpetually receding on the ecliptic, and must continue to do so while the earth exists. And the apsides, in like manner, are always moving forward in the same direction in which the planet moves.

It is worthy of notice, that while the mutual attractions of the planets disturb the orbits, they do not derange them. When the learner first considers the fact, that the sun and moon are perpetually pressing the equator of the earth towards the ecliptic, he is almost compelled to infer that it will be brought nearer and still nearer, until at length the two planes will coincide, and all distinction of seasons will disappear in every latitude of the earth. The sun will always culminate vertically at the equator; at the poles he will always be seen circulating about the horizon. But this calamitous derangement never can occur; the revolution on the axis prevents it. The combination of the two movements is, as we have seen, a simple retrocession of the equinoxes, which involves no change in the succession of sea

sons.

So, too, when the student of astronomy learns that the outer planets draw the earth away from the sun most of all at the aphelion, where it is already at the greatest distance, he seems to see this aphelion distance becoming greater and greater, as ages pass on, and the perihelion, of necessity, during the same ages, drawing nearer and nearer (as I move this ball in more and more eccentric ellipses about the lamp) until the condition of the earth's climate becomes fatal to every living thing. At the perihelion, the earth is subjected to an intolerable heat; at the aphelion, to a cold equally intolerable. But calculation and experiment both show, that the aphelion point, instead of being removed from the sun, by the attractions of the outer planets, will simply slide around, keeping its distance from the sun the same as ever. The planets have too much stability to be seriously deranged in respect to their orbits by the influence of outsiders.

This preservation of safe relations among the planets, in the midst of unceasing changes and disturbances, is one of the most interesting facts presented to the mind of the pupil in astronomy. He who made the countless spheres, ordained the laws of their motion; and those laws, by their perfect operation, secure the utmost peace and harmony, though worlds, thousands of miles in diameter, are rushing through

space with a velocity which it is fearful to contemplate. Huge as are these masses of matter, and terrific as are their velocities, they are perfectly controlled by their Omnipotent Lord, who subjects them to those few and simple laws with which we all have to do in the actions of every-day life.

[Since the delivery, in January last, of this ingenious and interesting lecture, the motions of the rotascope or gyrascope, as it is now called, has unexpectedly become a subject of general popular interest, and thousands of copies of a simple form of the instrument are now manufactured to gratify the public curiosity. The explanation of the principles of compound rotary motion is as old as the day of Newton, and the experimental illustrations given in this lecture have been annually exhibited by Professor Snell to his class in Amherst College for upwards of twenty years.

The following remarks may, perhaps, serve to make the brief explanation of Professor Snell of the horizontal rotation a little more easily understood. Suppose the horizontal axes (fig. 10) placed north and south, and the wheel revolving towards the east, then the particle A will tend to move eastward by the rotation and northward by the action of gravity; the resultant will therefore fall between these two directions, but much nearer the former, on account of the greater force. The tendency will therefore be to turn the plane of the disk outward, which, on account of the fixed position, of the point B, must carry the point D backwards. The same statement may be made with regard to the motion of the lower point of the disk, which conspires with the upper to produce a motion of the system in the same direction.

An interesting application of the principle of compound rotation has lately been made to the explanation of the lateral deviation of a ball from a rifle-bore cannon. The deviation is always in the same direction, and is the result of the same kind of action which produces the horizontal rotation of the system exhibited in the experiment (fig. 10) of the lecture. J. H.]

METEOROLOGY.

ABSTRACT OF OBSERVATIONS MADE DURING THE YEARS 1853, 1854, AND 1855, AT SACRAMENTO, CALIFORNIA.

BY THOMAS M. LOGAN, M. D.

GENERAL REMARKS,

The following observations and tables have been carefully drawn up and verified for future comparative reference. As the initiative of a series of more comprehensive and perfect observations, which it is proposed to prosecute for several successive years, they are now presented for record among the reports of the Smithsonian Institution. The increasing rigor which advancing physical science exacts before generalizations can be reliably deduced, especially requires the adoption of such a course, in a new country like this, possessed as it is of one of the most extraordinary climates known. In frequent instances discrepancies will be found between the present tables and those published in the reports for 1854, originating in errors of copy and typography, and which are now corrected. The barometric and thermometric computations are the result of three daily observations. Prior to April, 1854, they were made at 8 a. m., 3 p. m., and 10 p. m.; since that date, at sunrise, 3 p. m., and 10 m. P. Henceforth they will be continued, in accordance with the uniform system of observation adopted by the Smithsonian Institution, at 7 a. m., 2 p. m., and 9 p. m. The course of the wind was also noted three times a day, corresponding with the above periods, as well as the state of the weather in relation to clearness, cloudiness, and rain. By clear days, is meant entirely clear-i. e., no clouds whatever being visible at the time of observation; by cloudy, that some clouds were visible when it did not rain; and by rainy days, that more or less rain then fell without reference to quantity. The dew-point was taken at the driest time of the day only, (3 p. m.,) from July, 1854, to November, 1855, with Daniels' hygrometer; since then, it has been calculated from three daily observations with the wet and dry-bulb thermometer. The three tables of hourly observations for twenty-four successive hours, are the first of a series to be repeated four times every year, at or about the period of the solstices and equinoxes, for the purpose of determining the corrections to be applied, in order to render comparable with each other, the records made at different periods of the day. It will be perceived, in these "term observations," that the horary oscillations of the barometer present in a marked degree the two diurnal maxima and minima which obtain within the tropics. From a register kept with an extremely sensitive open-cistern barometer for six months, from the 1st of April, 1855, to September following, in

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clusive, for the express purpose of testing the regularity of the ebb and flow of the ærial ocean, it is ascertained that the mean monthly range between the sunrise and the 9 a. m. readings, amounted to 1.07 inch plus, in favor of the latter hour; whereas, between the 3 p. m. and the 94 p. m. readings, the mean monthly range was only 0.46 inch plus, in favor of the last hour. These observations will be continued for six months longer, in order to determine whether the fluctuations of atmospheric pressure occur as regularly in the same The instruments employed ratio and degree during the rainy season. were all placed in the open air on the north side of the lower story of a brick building, in a sheltered projection, and protected against the effect of either direct or reflected insolation, as well as against nocturnal radiation. In consequence of the care exercised in this respect, the figures of the thermometer ranged generally lower during the summer than those of other observers in the city. It is necessary to add, before proceeding to the special remarks for each year, that, according to recent observations by the Aneroid barometer, the altitude of the city may be put down at thirty-nine feet above tide-level. The latitude is 38° 34′ 42′′ north, and the longitude 121° 40′ 05" west.

REMARKS FOR 1853.

With the exception of the winter of 1849-'50, which, according to the representations of those who then resided here, was a season of almost continual rain-storms, that of 1852-'53 ranks thus far as the most notable for its high winds and heavy rains. The high northwest wind which set in a few days after the great fire in November, 1852, was succeeded by deluging rains, accompanied with strong wind from the southeast. The Sacramento river, which drains about 15,000 square miles before reaching the city, rose above its natural banks higher than was ever before known, converting the streets of Sacramento into flowing streams and bottomless quagmires. On the 1st of January the city was totally submerged. Dense fogs prevailed during the greater part of the days of the 3d, 4th, 13th, 14th, 17th, 18th, 19th, 20th, 21st, and 22d, which, in connexion with the predominance of southerly winds and the frequent fall of rain, caused a degree of humidity amounting almost constantly to saturation. February was comparatively a dry month. On the 5th the streets of Sacramento began to be passable, and in many points manifested indications of desiccation; while the river fell steadily, notwithstanding the rains towards the latter part of the month. On the night of the 22d there was a rain-storm from the southeast; after which date it rained more or less until the 25th, when it blew a gale from the southeast, with heavy rain at night. By the 6th of March the Sacramento river had fallen unusually low for the season, and the streets of the city, thus thoroughly drained, were drying up rapidly under the influence of a hot sun-the thermometer at 3 p. m. reading 75°. On the 8th heavy rains commenced falling again, and the weather continued variable to the end of the month. Nothing worthy of note occurred at the date of the equinox; but on the 28th, one of the heaviest rains ever measured here was found to have fallen, amounting to about five inches. On the following day the Sacramento river

was found to have risen twelve feet in twenty-four hours, overflowing its natural banks, and cutting off all communication with the interior by stages. On the 31st the American river, which empties into the Sacramento on the north side of the city, fell four feet in twenty-four hours; but the height of the Sacramento river remained unchanged, having attained within three inches of being as high as it was on the 1st of January.

April 1.-The river commenced backing up through a break in the levee at Sutterville, about two miles south of the city, and continued to rise at the rate of one inch per hour until the streets were again overflowed on the morning of the 2d. from the south commenced falling; the weather became genial, and On the 4th heavy warm rains vegetation began to burst forth. Notwithstanding the river began to fall slowly and steadily, it was still kept high by these spring showers. On the 13th, during a heavy shower from the south, vivid flashes of lightning, followed quickly by thunder, were witnessed; which phenomena also occurred on the 17th and 29th. At the latter date the rain was ushered in by a sprinkle of hail from a nimboid-cumulus from the southeast. The severest storm of the season occurred on the night of the 16th, the wind blowing a gale from the southeast, accompanied by rain.

May was unusually boisterous; high winds prevailing frequently from the south and southwest. The last shower of the regular rainy season occurred on the 20th. There was afterwards a sprinkle on the 28th and 29th. At the close of the month the river was within a few inches of the top of its natural banks, and still falling very slowly. June was the hottest month in the year, and was generally so throughout the State. On the 19th the barometer fell to the minimum of the month, lower than it was ever known, with the wind strong from the southeast. This uncommon disturbance of the equilibrium of the atmosphere was followed by no other appreciable effects here than a considerable moderation of temperature, and a brisk shower of rain on the 26th; an unusual occurrence in June. The mean temperature was 80° when the sun entered Cancer, and the mean reading of the barometer was 29.25 inches: weather clear, and wind veering from south to northwest.

July was rendered most agreeable by a greater proportion of relative moisture in the atmosphere than is usually found during midsummer, and which may be attributed to the prevalence of southeast winds. Two sprinkles of rain-one on the 17th and the other on the 21st-occurred this month. That on the 17th happened about sunset, when a beautiful rainbow was refracted.

August was characterized by remarkably cool nights. The minima observed on the nights of the 13th and 31st were 51° and 50° respectively.

September was comparatively a sultry month; the wind being generally very light, particularly during the last four days. A brisk shower of rain occurred at daylight on the 15th, with the wind from southwest, and the barometer reading 29.90 inches. On the 22d, the mean reading of the barometer was 30.05 inches, and of the thermometer 74°: sky clear, and wind southerly and light.

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