refined, and the highest range of mathematics on the other. Rittenhouse first suggested the true explanation of the experiment, of the apparent conversion of a cameo into an intaglio, when viewed through a compound microscope, and anticipated many years Brewster's theory. Hopkinson wrote well on the experiment made by looking at a street lamp through a slight texture of silk. Joscelyn, of New York, investigated the causes of the irradiation manifested by luminous bodies, as for instance the stars. Of late, photographic experiments have occupied much attention, and Draper has advanced the bold idea, supported by experiment, that the agent in the so-called photography, is not light, nor heat, but an agent differing from any other known principle. Henry has investigated the luminous emanation from lime, calcined with sulphur, and certain other substances, and finds that it differs much from light in some of its qualities.
Astronomy is the most ancient and highest branch of physics. One of our earliest and greatest efforts in this branch was the invention of the mariner's quadrant, by Godfrey, a glazier of Philadelphia. The transit of Venus, in the last century, called forth the researches of Rittenhouse, Owen, Biddle, and President Smith, near Philadelphia, and of Winthrop, at Boston. Two orreries were made by Rittenhouse, as also a machine for predicting eclipses. Most useful observations, connected with the solar eclipses, from 1832 to 1840, have been made by Paine, of Boston. We have now well-supplied observatories at West Point, Washington, Cambridge, Philadelphia, Hudson, Ohio, and Tuskaloosa, Alabama; and the valuable labors of Loomis, Bartlett, Gillis, Bond, Pierce, Walker, and Kendall are well known. Mr. Adams, so distinguished in this branch and that of weights and measures, laid last year the corner stone of an observatory at Cincinnati, where will soon be one of the largest and most powerful telescopes in the world. Most interesting observations as to the great comet of 1843 were made by Alexander, Anderson, Bartlett, Kendall, Pierce, Walker, Downes, and Loomis, and valuable astronomical instruments have been constructed by Amasa Holcomb, of Massachusetts, and Wm. J. Young, of Philadelphia.
It is difficult to class the brilliant meteors of November the 13th, 1833. If such meteors are periodic, the discovery was made by Professor Olmsted; and Mr. Herrick, of New Haven, has added valuable suggestions. The idea that observers, differently placed at the time of appearance and disappearance of the same meteor, would give the means of determining differences of longitude, was first applied in our own country, where the difference of longitude of Princeton and Philadelphia was determined by observations of Henry and Alexander, Espy and Bache. In meteorology our countrymen have succeeded well. Dr. Wells, of South Carolina, elaborated his beautiful and original theory of the formation of dew, and supported it by many well-devised and conclusive experiments. The series of hourly observations, by Professor Snell and Captain Mordecai, are well known; and the efforts of New York and Pennsylvania, of the medical department of the army, and its present enlightened head, Dr. Lawson, have much advanced this branch of science. The interesting question, Does our climate change? seems to be answered thus far in the negative, by registers kept in Massachusetts and New York. There are two rival theories of storms. That of Redfield, of a rotary motion of a wide column of air, combined with a progressive motion in a curved line. Espy builds on the law of physics, examines the action of an upmoving column of air, shows the causes of its motion and the results, and then deduces his most beautiful theory of rain and of land and water spouts. This he puts to the test of observation; and in the inward motion of wind toward the centre of storms, finds a striking verification of his theory. This theory is also sustained by the overthrow or injury, in the recent tornado at Natchez, of the houses whose doors and windows were closed, while those which were open mostly escaped unhurt. Mr. Espy must be considered, not only here, but throughout the world, as at the head of this branch of science. This subject has been greatly advanced by Professor Loomis, whose paper has been pronounced, by the highest authority, to be the best specimen of inductive reasoning which meteorology has produced. The most recent and highly valuable meteorological works of Dr. Samuel Forry are much esteemed. Many important discoveries in pneumatics were made by Dr. Franklin and Count Rumford, and the air pump was also greatly improved by Dr. Prince, of Salem.
Chemistry, in all its departments, has been successfully pursued among us. Dana, Draper, Ellet, Emmet, Hare, the Mitchells, Silliman, and Torrey, are well known as chemical philosophers; and Booth, Boyé, Chilton, Keating, Mather, R. Rogers, Seybert, Shepherd, and Vanuxen, as analysts; and F. Bache, Webster, Greene, Mitchell, Silliman, and Hare, as authors. In my native town of Northumberland, Pennsylvania, resided two adopted citizens, most eminent as chemists and philosophers, Priestley and Cooper. The latter, who was one of my own preceptors, was greatly distinguished as a writer, scholar, jurist, and physician, as well as a chemist. Priestley, although I do not concur in his peculiar views of theology, was certainly one of the most able and learned of ecclesiastical writers, and possessed also a mind most vigorous and original. His discoveries in pneumatic chemistry have exceeded those of any other philosopher. He discovered vital air, many new acids, chemical substances, paints, and dyes. He separated nitrous and oxygenous airs, and first exhibited acids and alkalies in a gaseous form. He ascertained that air could be purified by the process of vegetation, and that light evolved pure air from vegetables. He detected the powerful action of oxygenous air upon the blood, and first pointed out the true theory of respiration. The eudiometer, a most curious instrument for fixing the purity of air, by measuring the proportion of oxygen, was discovered by Dr. Priestley. He lived and died in my native town, universally beloved as a man, and greatly admired as a philosopher. Chemistry has actively advanced among us during the present century. Hare's compound blowpipe came from his hand so perfect, in 1802, that all succeeding attempts of Dr. Clark, of England, and of all others, in Europe and America, to improve upon it or go beyond the effects produced, have wholly failed. His mode of mixing oxygen and hydrogen gases, the instant before burning them, was at once simple, effective, and safe. The most refractory metallic and mineral substances yielded to the intense heat produced by the flame of the blowpipe. In chemical analysis, the useful labors of Keating, Vanuxen, Seybert, Booth, Clemson, Litton, and Moss, would fill many volumes. In organic chemistry, the researches of Clark, Hare, and Boyé were rewarded by the discovery of a new ether, the most explosive compound known to man. Mitchell's experiments on the penetration of membranes by gases, and the ingenious extension of them by Dr. Rogers, are worthy of all praise. The softening of indiarubber, by Dr. Mitchell, renders it a most useful article. Dyer's discovery of soda ash yielded him a competence. Our countrymen have also made most valuable improvements in refining sugar, in the manufacture of lard oil and stearin candles, and the preservation of timber by Earle's process. Sugar and molasses have been extracted in our country from the cornstalk, but with what, if any profit, as to either, is not yet determined. No part of mechanics has produced such surprising results as the steam engine, and our countrymen have been among the foremost and most distinguished in this great and progressive branch. When Rumsey, of Pennsylvania, made a steamboat, which moved against the current of the James River four miles an hour, his achievement was so much in advance of the age, as to acquire no public confidence. When John Fitch's boat stemmed the current of the Delaware, contending successfully with sail boats, it was called, in derision, the scheme boat
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