magnetic effects; and also of forming and decomposing chemical compounds.

But investigation has gone still further. It is found that all these changes take place in rigorous accordance with the laws of quantity. As matter cannot be destroyed, neither is force capable of destruction; and as matter may be pursued through all its multitudinous changes without loss, the same principle is found to hold in regard to force. It has long been familiarly known that machines do not create force, but only communicate, distribute, and apply that which is imparted to them. In all cases the force expended is exactly measured by the resistance overcome. In the case of water-power, to lift a hammer of 100 pounds one foot high at least 100 pounds of water must fall through one foot; or, what is the same thing, 200 pounds must fall through half a foot, or 50 pounds through two feet. If a hammer weighing 1,000 pounds is employed with the same driving force, it will either be raised to only onetenth the height, or, tenfold the time will be required to raise it the same height. Thus in machines a certain amount of power acting as cause, produces an exactly equal amount of change, as effect.

It is precisely the same when the molecular forces are involved-those forces which involve the agency of atoms. It is well understood that a certain amount of fuel is necessary to perform a given amount of work with a steam engine. This means, strictly, that definite quantities of the chemical action of combustion give rise to a fixed quantity of heat, and this to a determinate quantity of mechanical effect. Dr. Faraday made the important discovery of the definite chemical effect of the voltaic current. He found that an equivalent of an element consumed in a battery gives rise to a definite quantity of electricity which will produce exactly an equivalent of chemical decomposition. For example, the consumption of 32 grains of zinc in the battery excites a current which will set free from combination 1 grain of hydrogen, 104 of lead, 108 of silver, 39 of potassium, and 31.6 of copper. But these are the combining numbers of those elements, and thus is established a remarkable equivalency between chemical and electrical forces.

That a certain amount of heat produces a definite quantity of mechanical force has been long known; but only lately has the question been inverted: how much heat is produced by a certain amount of mechanical force? The answer to this question gives rise to the science of thermodynamics. All friction, collision, and condensation, whether of solids, fluids, or gases, produce heat. But to ascertain at what rate mechanical force produces heat it requires certain standards of comparison known as the units of heat and force. The English unit of heat is one pound of water, raised through 1° F. The unit of force is one avoirdupois pound falling through one foot of space. By a great

number of experiments, Dr. Joule of Manchester, Eng., demonstrated the mechanical equivalent of heat-that is, how many units of force are equal to a unit of heat. He agitated water, mercury, and oil successively in suitable vessels, by means of paddles driven by falling weights, and determined the exact amount of heat produced, and the force spent. By varied and repeated operations, conducted with consummate skill and great patience, he found that the same expenditure of power produced the same absolute amount of heat, whatever materials were used; and that a pound weight falling through 1 foot, and then arrested, would produce a unit of heat, that is sufficient to raise 1 lb. of water 1° F. The vast significance of this fact to science is obvious; every movement that takes place throughout the universe, whether of molecules or masses, has its fixed thermal value-it represents and may be converted into a definite amount of heat.

The imponderables, then, have passed away, with the epicycles of the old astronomers and the phlogiston of the old alchemists-monuments of the past progress of thought—and we have in their stead pure forces which are all varying modes of motion of ordinary matter. Science assumes the atomic constitution of matter; that there are interspaces between the atoms, and that these atoms are capable of various motions, and are probably in a state of constant movement. They may rapidly oscillate backward and forward, or whirl upon their axes, or even revolve through orbits, like what we may term the larger atoms of the solar system. Perhaps they execute several of these movements at the same time as do the planets. They are also believed to be endowed with polarities, and that their motions are subject to a polar control. Each molecular force is regarded as a mode of motion among the atoms; and as these motions may pass into each other the forces are convertible. Heat is that mode of motion among atoms by which they are caused to move further apart, producing expansion of the mass, or heating it. As the motion declines the body contracts and cools. Heat is produced by friction or collision because the mechanical motion which is arrested and disappears is changed to the molecular motion of the mass; while the mechanical motion produced by heat, as in the case of the steam-engine, is simply the consequence of the translation of atomic movement into massive motion. No force can be annihilated, and what the atoms lose, the mass gains.

Caloric, the electric fluid, and luminous corpuscles are denied; yet science still holds to the conception of a universal ether. Some writers, prominent among whom is Mr. Grove, protest against this as an inadmissible assumption. They say we can neither make nor prove the existence of a perfect vacuum, and, therefore, are not entitled to deny that matter is universal. There may be, and there probably is, matter, in some form, however attenuated,

everywhere; and, so long as there is a universal material vehicle for motion, the conception of a hypothetical ether is superfluous. But it is replied that, by the term ether, is meant this universal material, something capable of motion, and assumed to possess certain definite properties. Some such conception is necessary at the present time, in order to express those systems of movement in which the various forces consist.

As thermometric heat, or the heat of conduction, is a motion of the constituent atoms of bodies, so radiant heat, or that which darts forward rapidly in straight lines, is a movement of the ether. Light is no longer the shooting of corpuscular particles; it is a certain rate of undulation of the ethereal medium -it is motion. The different colors result from different rates of undulation. The various actinic, or chemical rays, are due to the same cause, and thus there is seen to be a close correlation between the radiant forces; they are all but modes of motion. The vibrations of the atoms may impart motion to the ether as it occurs in the radiation of every heated body; and, conversely, the undulations of the ether may be spent in setting the particles of bodies in motion, and thus bodies are warmed by radiation.

The most recent and important step in the progress of thermotic science has been made by Prof. Tyndall, and consists of an analysis of the relations of radiant heat to gaseous bodies, and especially to water vapor. We condense from the new edition of Youmans' Chemistry, in which the recent views are fully developed, a statement of the principles involved in this subject. An opaque body destroys the luminous waves which fall upon it; while a transparent one permits them to glide through between the atoms without interference. But there are bodies which destroy some of the waves and allow others to pass. If a piece of red glass be placed between the prism and the spectrum it stops the blue rays and transmits only the red-that is, it cuts down the more minute waves and gives passage only to the larger. If blue glass be used there is a reverse effect, the red rays being extinguished and the blue alone transmitted. Both glasses are transparent, yet, if placed together in the path of the rays, they are as opaque as a plate of iron, each destroying what the other transmits. This is also the case with the heat rays; they are of different kinds like the colors of light, and are arrested and transmitted differently by different substances. Rock salt is the most perfect diathermic body; that is, it allows all the heat rays, those from the sun and from the hand to pass through with equal freedom. Glass and a thin film of water will absorb or arrest the dark or obscure radiations, while they will pass luminous heat or those radiations which come from a luminous source. It is well known that the sunbeam is a bundle of heterogeneous radiations, and that the prism

spreads them out into a spectrum, thermal at one end, chemical at the other, and luminous in the centre. The same thing holds true of all sources of heat, luminous and obscurethey emit rays of different qualities. When the mixed rays from any source are passed through a plate, a certain portion of them is stopped, and another portion transmitted. But if the rays that are passed are made to fall upon a second similar plate, a much larger portion will be transmitted than went through the first the first plate sifted the ray, and the purified beam is better fitted to penetrate another similar plate. This principle explains the fact that glass readily transmits solar heat, while it stops the heat from a red-hot cannon ball in large quantities. The rays of the sun in coming through the atmosphere are strained of those rays which would be stopped by glass, so that the altered beam passes our windows without loss.

Tyndall's apparatus for investigating the influence of gases upon radiant heat, consisted of a long glass tube three inches in diameter, closed air tight at either end by caps of pure rock salt, and connected with apparatus so as to be exhausted and filled with various gases at pleasure. At one end of the tube was placed his source of heat, a blackened canister of hot water, and at the other end a thermo-electric pile-the most delicate instrument for measuring or detecting heat. By this machine, controlled so carefully as to secure the utmost precaution against error, Tyndall exposed various gaseous bodies to the dark thermal radiations. Purified air was found to arrest none or an exceedingly minute proportion of the rays; while pure oxygen, hydrogen, and nitrogen behave in a similar manner, being almost neutral. But when compound gases were introduced, there was a remarkable effect: olefiant gas, which is just as transparent as air, arrests 80 p. c. of the rays of heat. Pure transparent ammonia is still more impenetrable and stops the heat as light would be stopped if the cylinder were filled with ink. The same effect is produced if only a small proportion of these gases is mingled with the air of the cylinder.

In this manner, invisible gases become the means of sounding the atomic constitution of bodies. While heat rays pass through common oxygen without being intercepted, ozone, which is but another form of oxygen, arrests a large proportion of it like compound gases; we therefore infer that its atoms are arranged in groups or complex molecules. When aqueous vapor was introduced into the tube, it was found to be highly opaque to the dark radiations. Where the atmospheric gases arrest one ray of obscure heat, the small proportion of watery vapor contained in the air strikes down sixty or seventy rays. The consequences of this fact are in every way of the highest importance in the economy of nature. Luminous heat from the sun penetrates the air, and falling upon the

earth, is changed into obscure heat which is intercepted by the watery vapor of the atmosphere, and cannot therefore be radiated back again into space. The atmospheric vapor is therefore the means of maintaining the earth's temperature, and if it were withdrawn from the air, the loss of terrestrial heat would soon render the earth uninhabitable. In all those localities where the atmosphere is dry, the nightly loss of radiant heat is so great, that even in the burning desert of Sahara there is nocturnal freezing.

The aqueous vapor contained in the air exists mostly in its lower strata near the ground. The upper portions of the atmosphere are comparatively dry. Hence, high mountains being raised above the zone of watery vapor, are unprotected, and their heat consequently streams away into space with such rapidity that the temperature sinks to a low degree. As the winds dash against the frigid mountain peaks, their moisture is rapidly condensed and frozen into snow-hence the everlasting snow of these lofty land summits. In these circumstances, where the snow falls incessantly in large quantities, it is condensed into ice, and slowly creeps down the valleys in the form of vast rivers of ice known as glaciers. We thus see how the relations of radiant heat to aqueous vapor afford an explanation of the magnificent phenomena of snow peaks and glacial action. The ultimate cause of all these effects is of course that solar heat which originally changed the water into the vaporous form. The heat thus absorbed must again escape in condensation, while the grand function of the mountains appears as that of condensers. Each fragment of glacial ice is to be regarded as the product of the heat spent in first evaporating its water, and in this point of view the glaciers represent an amount of heat equal to five times their weight of melted cast iron. In connection with these important discoveries of the opacity of gases to radiant heat, Prof. T. Sterry Hunt has called attention to the effect which a large proportion of carbonic acid in the earth's ancient atmosphere must have had in preserving the high temperature of the earth.

The consummate series of investigations by which these results were reached, is admirably described by Dr. Tyndall, in his late work on heat, in which the new views of the nature of heat itself are applied with great skill and ingenuity to many of the phenomena of nature.

The history of the dynamical theory of heat is deeply interesting, as throwing a striking light on that action of the human mind which leads to great discoveries of the laws of nature. It illustrates, in a remarkable manner, that great truths are growths of time, and that discoveries oftener belong to epochs than to individuals. As far back as the time of Bacon, we find statements concerning heat which contradicted the common view, and which are susceptible of easy interpretation, in harmony with the recently established views. In the twen

tieth aphorism of the second book of the Novum Organon, its illustrious author remarks: "Now from this our first vintage, it follows that the form, or true definition of heat (heat, that is in relation to the universe, not simply in relation to man), is in a few words as fol lows: Heat is a motion, expansive, restrained, and acting in its strife upon the smaller particles of bodies, but the expansion is thus modified: while it expands all ways, it has at the same time an inclination upward. And the struggle in the particles is modified also; it is not sluggish, but hurried, and with violence." Again, the philosopher Locke remarks: "Heat is a very brisk agitation of the insensible parts of an object, which produces in us that sensation from which we denominate the object, but so that what in our sensations is heat, in the object is nothing but motion." But the first experimental step in this direction of thought, and perhaps the grandest step taken by any single mind, was made by an American, Benjamin Thompson, afterward known as Count Rumford. He went to Europe in the time of the revolution, and devoting himself to scientific investigations, became the founder of the Royal Institution of England. He exploded the notion of caloric, demonstrated experimentally the conversion of mechanical force into heat, and arrived at quantitative results, which, considering the roughness of his experiments are remarkably near the established facts. He revolved a brass cannon against a steel borer by horse power, for two and a half hours, and generated heat enough to raise 181⁄2 lbs. of water from 60° to 212.° In his paper read before the Royal Society, in 1798, he observes: "From the results of these computations, it appears that the quantity of heat produced equally in continuous stream, if I may use the expression, by the friction of the blunt steel bar against the bottom of the hollow metallic cylinder, was greater than that produced in the combustion of nine wax candles, each of an inch in diameter, all burning together with clear bright flames." Rumford explicitly announced the view now held of the nature of heat and wrote as follows, the italics being his own: "What is heat? Is there any such thing as an igneous fluid? Is there anything that with propriety can be called caloric? We have seen that a very considerable quantity of heat may be excited by the friction of two metallic surfaces, and given off in a constant stream or flux in all directions. Without interruption or intermission, and without any signs of diminution or exhaustion. In reasoning upon this circumstance, we must not forget that most remarkable circumstance, that the source of the heat generated by friction in these experiments, appeared to be inexhaustible. It is hardly necessary to add that anything, which any insulated body or system of bodies can continue to furnish without limitation, cannot possibly be a material substance; and it appears to me to be extremely difficult, if not quite impossible, to

form any distinct idea of anything capable of being excited, and communicated in these experiments except it be MOTION."

Sir Humphrey Davy, the associate of Rumford, in the Royal Institution, adopted these views concerning heat. He instituted some delicate experiments by which they were strikingly confirmed. One of these consisted in rubbing two pieces of ice together in a vacuum, at a temperature below the freezing point. The heat of friction melted the ice. The old explanation of the fact was that the friction liberated the latent caloric of the ice. To this, Davy replied: "If I by friction liquefy ice, Í produce a substance which contains a greater absolute amount of heat than the ice; and in this case it cannot with any show of reason be affirmed, that I merely render sensible the heat hidden in the ice, for that quantity is only a small fraction of the heat contained in the water." Davy also propounded the hypothesis of atomic vibrations or oscillations, as the cause of thermal phenomena. This cannot be better stated than in his own words: "It seems possible to account for all the phenomena of heat, if it be supposed that in solids the particles are in a constant state of vibratory motion, the particles of the hottest bodies moving with the greatest velocity, and through the greatest space; that in fluids and elastic fluids, besides the vibratory motion, which must be conceived greatest in the last, the particles have a motion round their own axes with different velocity, the particles of elastic fluids moving with the greatest quickness, and that in ethereal substances the particles move round their own axes, and separate from each other, penetrating in right lines through space. Temperature may be conceived to depend upon the velocity of vibrations; increase of capacity in the motion being performed in greater space; and the diminution of temperature during the conversion of solids into fluids or gases, may be explained on the idea of the loss of vibratory motion, in consequence of the revolution of particles round their axes, at the moment when the body becomes fluid or aëriform, or from the loss of rapidity of vibration in consequence of the motion of the particles through space."

The researches of Davy upon this subject may be regarded as continuing those of Count Rumford. In 1812 he wrote: "The immediate cause of the phenomena of heat, then, is motion, and the laws of its communication are precisely the same as the laws of the communication of motion." Seguin in 1819 published a work entitled De l'Influence des Chemins de Fer, in which he shows that the old theory leads to the absurd conclusion, that a limited quantity of heat can produce an unlimited quantity of chemical action. He says: "It appears to me more natural to suppose that a certain quantity of caloric disappears in the very act of the production of the force or mechanical power, and reciprocally the mechanical

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force which disappears during the lowering of the temperature of a gas is the measure and the representation of the elimination of heat."

The time had now arrived for the reception of these views by many minds, and accordingly we find that, during the next ten years, eminent scientific men in England, France, Germany, Denmark, and America, devoted themselves with assiduity to their theoretical and experimental development. In 1850 Joule's law was established, which placed the subject upon an immovable experimental basis. While, during the same year, Dr. Carpenter formally extended the research so as to include the vital forces. His paper on the correlation of the physical and vital forces, was published in the philosophical transactions for that year. From that time, the views have been gradually accepted by scientific men, until they may now be regarded as generally established. Science has thus changed her standpoint, and all phenomena are presented in a new light. The most important results alike to science, philosophy, and education, may be expected to follow this revolution of scientific thought.

HILDRETH, SAMUEL PRESCOTT, M. D., an American historian and physicist, born in Methuen, Massachusetts, Sept. 30th, 1783, died at Marietta, Ohio, July 24th, 1863. His boyhood was passed on his father's farm, until he was fifteen years old, his primary education being received at a common school. From thence he was sent to Phillips Academy, Andover, and the Franklin Academy, in the North Parish. He studied medicine with Dr. Thomas Kittridge, a noted surgeon of Andover, and received a diploma from the Medical Society of Massachusetts in Feb., 1805. He commenced the practice of his profession in New Hampshire, but, in 1806, having made up his mind to settle in Ohio, journeyed thither on horseback, and after spending about two months in Marietta, located himself at Belpre, where, in 1807, he married Miss Cook (formerly of New Bedford, Mass.). He was very successful in practice; but, in 1808, removed to Marietta, where the duties of his profession were less arduous, and where he remained to the close of his life. In 1810 and 1811 he served in the Ohio Legislature as a supporter of the administrations of Jefferson and Madison; but on the formation of the republican party, in 1854, he connected himself with it. For a period of nearly forty years he was a contributor to "Silliman's Journal of Science," his articles embracing a wide range of scientific subjects, but more especially devoted to meteorology, geology, and paleontology. In 1837 he was a member of the Geological Survey, and delivered the annual address at Cleveland, before the Medical Society, of which he was then president, giving a history of the diseases and climate of Southeastern Ohio, from its settlement, which was published by the Society. The same year he published a history of the settlement of Belleville, Western Vir

ginia, in the "Hesperian," a magazine published in Cincinnati. In 1848 he prepared his "Pioneer History," an account of the first examinations of the Ohio valley, and early settlement of the Northwest Territory, which, with his "Lives of the Early Settlers of Ohio," were published under the auspices of the Ohio Historical Society; both works of great value. In 1830 he commenced the collection of a cabinet of natural history, and in the course of eight years had gathered more than 4,000 specimens, arranged, classified, and catalogued, and all this without interfering with the duties of his profession. He collected also more than 5,000 shells, some of which he exchanged for books of a scientific nature, thus enabling him in time to form a large and valuable scientific library, which, previous to his death, he donated, together with his cabinet, to Marietta College. He was in the enjoyment of good health and remarkably active in all his movements until a fortnight preceding his death.

HOLSTON RIVER. This is the largest branch of the Tennessee river. It is formed by the junction of the north and south forks which rise among the Alleghany Mountains of Virginia, and unite at Kingsport, Sullivan county, Tennessee. Flowing thence and passing Knoxville, in East Tennessee, it unites with the Clinch river, at Kingston. The length of the main stream is estimated at two hundred miles. It is navigable by small steamboats to Knoxville, and during the winter they can ascend to Kingsport.

HOPE, GEORGE WILLIAM, M. P., born at Blackheath in 1808, died at Suffness, Haddingtonshire, October 18th, 1863. He was a son of the Hon. Alexander Hope, was educated at Christ Church, Oxford, and called to the bar at Lincoln's Inn, in 1831. The death of an elder brother, however, altered his position, and removed him from the ranks of practising barristers. Soon after, his attention was turned to politics, and in 1837 he was elected for Weymouth. In 1842 he was returned for Southampton, and became Under Secretary for the Colonies, an appointment which he held until the retirement of Lord Stanley, the Colonial Secretary, in December, 1845. In 1859 he again came forward, and was chosen for New Windsor as a supporter of the Derby Administration. He retained his seat until his death.

HOPE, Admiral Sir HENRY, K. C. B., born in 1787, died at Holly Hill, Hampshire, September 23d, 1863. He entered the navy in the spring of 1798, as midshipman, became lieutenant in 1804, and captain in 1808. He served in the Mediterranean on board the "Kent," and was afterward transferred to the "Swift sure," and was on that ship when she was taken a prize by a portion of the French squadron which had escaped from Toulon. In 1815, he was in command of the "Endymion," forty gun frigate, and distinguished himself in the engagement with the American ship "Presi

dent," which he took as a prize to Spithead, and was presented by the admiralty with a gold medal, and the nomination of a Companion of the Order of the Bath. He was successively advanced to the rank of rear-admiral, vice-admiral, and admiral, and was also aidede-camp to William IV., and to her Majesty. In July, 1855, he was nominated a Knight Commander of the Order of the Bath. He left personal property to the amount of £70,000, nearly one half of which he bequeathed to various religious and charitable societies.

HUBBARD, JOSEPH STILLMAN, an American astronomer, born at New Haven, Conn., in 1823, died in that city August 16th, 1863. He graduated with high honor at Yale College, in 1843, giving evidence of extraordinary mathematical ability, and in the spring of 1844 was appointed an assistant to the late distinguished astronomer, Sears C. Walker, in the High School Observatory, Philadelphia. In the autumn of the same year he was employed by Captain (now Major-General) Fremont to reduce his Rocky "Mountain Observations," and was invited to accompany him on his next expedition. Declining this offer, he was, at the instance of Col. Fremont and Senator Benton, appointed by Hon. George Bancroft, then Secretary of the Navy, a professor of mathematics in the U. S. Navy, and assigned to duty in the Naval Observatory, then just established at Washington. This post he filled with remarkable zeal and fidelity to the time of his death. The printed volumes of the Washington Observations are full of the evidences of his skill as an observer and a computer. Professor Hubbard was a frequent and valued contributor to the "Astronomical Journal." His investigations on Biela's comet, and on the great comet of 1843, are recorded in that journal in a series of elaborate papers. He also contributed papers on the orbit of Egeria, and many other topics. The article "Telescope," in the New American Cyclopædia, a paper of great labor and research, was also from his pen. labors of love in the cause of benevolence and religion were not less zealous than in the paths of science.

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of

HUNT, Major EDWARD B., an officer of U. S. volunteers, born in Livingston county, N. Y in 1822, died at the Brooklyn Marine Hospital, Oct., 2d, 1863. He was appointed to the Military Academy from his native State in 1841, graduated second in the class of 1845, was appointed second lieutenant in the corps engineers, and was assigned to duty as assistant to the Board of Engineers for Atlantic Coast Defence. After serving in this capacity a year, he was called to fill the important position of principal assistant professor of civil and military engineering at the Military Academy, West Point, where he remained until 1849, when he was employed as assistant-engineer upon Fort Warren, Boston harbor, Mass. From 1851 to 1855 he was the assistant of Prof. Bache, in the Coast Survey Bureau. From