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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, con- . trolled 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

ticth 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 upen 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, Berjamin 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 torer by horse power, for two and a half hours, and generated heat enough to raise 184 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 a 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

VOL. III-32 A

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 Hiil, Hampshire, September 23d, 1863. He entered the navy in the spring of 1798, as midshipman, became lieutenaut in 1804, and captain in 1808. He served in the Mediterranean on board the "Kent," and was afterward transferred to the "Swiftsure," 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

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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. His labors of love in the cause of benevolence and religion were not less zealous than in the paths of science.

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 of 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

1855 to 1857 he was engaged in the engineering operations in Newport harbor, R. I., and constructed and repaired many important lighthouse structures on the coast. In 1857 he was ordered to Key West, where, for five years, he assisted in the construction of fortifications and other defensive works on that island, receiving his captaincy while serving there, July 1st, 1859. It was chiefly through his instrumentality that the forts of Southern Florida were withheld from the Confederates after the war actually commenced. In 1862 he was appointed chief-engineer of the 5th army corps, commanded by Major-General Banks, and from this duty was relieved and placed on special service under the Navy Department, in order to superintend the construction of his submarine battery, an invention of his own, which he was sanguine would successfully defeat any naval attacks which might be made by the most powerful fleets upon our harbors. While engaged in making some experiments with this battery, a shell prematurely discharged, imme diately after which he descended into the caisson, and, in attempting to ascend, being probably overcome by the gas, fell backward, striking his head and causing concussion of the brain, from which he died the following day. Major Hunt was a brother of ex-Governor Washington Hunt of New York, and was a man of great ability and scientific attainments, and a frequent and valued contributor to the transactions of the American Association for the Advancement of Science, and to various literary and scientific works of the country. He was a man of sincere patriotism, and thoroughly conscientious in the discharge of his duties as an officer and as a man.

HYGIENE IN THE ARMY. The regular army of the United States, before the commencement of the present war, seldom numbering in its ranks more than 12,000 or 13,000 men, and with a medical and hospital service corresponding to its limited numbers, had little need of special rules of hygiene, or the elaboration of any extensive system of regulating the health and physical comfort of its forces. But when a volunteer army of more than half a million of men was suddenly called into existence, men, too, to whom camp life was an entirely new experience, who had for the most part little or no knowledge of the art of cookery, or of the thousand causes of disease which lurked in their new mode of life, in the climate, exposure, over exertion, unsuitable or insufficient food, clothing, &c., it became evident that it required fully as much medical skill and care to prevent disease as to effect a cure when it had made its appearance. The medical department of the Government, aided in this matter most effectually by the Sanitary Commission, found it necessary to give special instruction to the army surgeons, whether engaged in examining recruits or in service on the field or in the hospitals, in matters relating to the hygienic condition of the force; and

during the past year, in addition to monographs on particular branches of the subject by subcrdinate medical officers of the army, the accomplished surgeon-general has, by the most indefatigable industry, found or made leisure to prepare an admirable treatise on "Hygiene in the Military Service."

* * * *

The first step in the way of prevention of disease in the army must be taken in the examination of recruits. The ignorance or incompetence of the examining surgeons in the first two years of the war, and sometimes it is to be found baser motives, led to great abuses in this respect. "Thousands of incapacitated men," says Surgeon-General Hammond, "were, in the early stages of the war, allowed to enter the army, to be discharged after a few weeks' service, most of which had been passed in the hospital. Many did not march five miles before breaking down, and not a few never shouldered a musket during the whole time of their service. Cases of chronic ulcers, varicose veins, epilepsy, and other conditions unfitting men for a military life, came frequently under my notice. The recruits were either not inspected at all by a medical officer, or else the examination was so loosely conducted as to amount to a farce. I know of several regiments in which the medical inspection was performed by the surgeon walking down the line and looking at the men as they stood in the ranks." There has been great improvement in these examinations since the autumn of 1862, but even now too many men unfit for the service are smuggled into it, through the lack of vigilance on the part of the inspector. The enlistment of weak, malformed, or sickly soldiers is a great crime against the service. The soldier, to be capable of serving his country effectively in the field, requires not only sound health but the ability to endure fatigue, hardships, exposure, and vicissitudes of climate with impunity. To admit into the ranks a soldier who does not possess this ability, inflicts upon the army not only the probable loss of his services, very often at a time when they are most needed, but, if he is consigned to a hospital, requires the care of others for his nursing, who might otherwise be employed in the national defence. The minimum age at which volunteers are received (eighteen years, and in many cases by the connivance of examining officers, below that age) is too young for serviceable soldiers. These young recruits break down under the severe marches and privations of the camp, and are more liable to those terrible scourges of the army, diarrhoea and dysentery, as well as to a fatal termination of wounds than those who enter the army at twenty or over. The height of the recruit (our minimum limit is five feet three inches, and there is no maximum, as there should be), the capacity of the chest, vigor of the system, and general aptitude for the soldier's profession, are all points of great importance, and must be carefully examined by

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