USA > Maine > York County > Parsonsfield > A history of the first century of the town of Parsonsfield, Maine > Part 13
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To set forth the subsequent growth and development of the telegraph would require a volume. It will not be amiss, however, to call attention to the fact that whereas in the early days of the telegraph it was thought necessary to have as many wires as there are letters in the alphabet in order to send a single message, it is now possible to send as many messages over a single wire simultaneously as there are letters, and without confusion. The details of the several devices by means of which these results may be accomplished are too complicated for pre- sentation here.
Hardly less remarkable is the fact that one may now have his message de- livered printed in roman character just as it comes over the wires.
The submarine cables which now encircle the earth in various directions and bring us news from the uttermost parts of the world, even before the date of its happening, have ceased to be matters of surprise. Their effects, however, have proved to be more than commercial and political in their character. It is to the , difficulties which beset their construction and operation that we owe some of the most brilliant achievements of science.
In 1837, while Morse was experimenting with his telegraphic apparatus, a dis- covery was made in Baltimore, by Page, which was destined at a later period to
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open the way to greater marvels than the telegraph can ever exhibit. Page found that when a rod of iron is suddenly magnetized and demagnetized, by passing a current of electricity through a coil of insulated wire containing it, it emits a sound. It was afterwards found by Wertheim that this is due to the sudden deformation of the iron rod.
These facts being known to Philipp Reis, a young school master at Friedrichs- dorf near Homburg, he thought to utilize them in the construction of a telephone by means of which articulate speech itself might be transmitted over a conduct- ing wire. The receiver at which the ear was to be placed consisted of a small steel rod placed in the interior of a coil of insulated wire, the extremities of the rod being supported by a " sounding board" covering a small box of resonant wood. The transmitting apparatus, or that against which the voice of the speaker is to be directed, consists of a membrane stretched tightly so as to vibrate when acted on by the particles of air set in motion by the sound, and of certain accessories. These are a piece of platinum attatched to the middle of the membrane so as to be carried by it, and, in connection with the line wire, another piece of platinum resting lightly on first by means of a spring or by gravity, also connected to the line. When the circuit between the speaker and the listener is joined including this apparatus, the receiving apparatus just described and a battery, and the voice, in singing or speaking, is directed against the membrane of the transmitting apparatus, the contact between the pieces of platinum is made to vary with the motion of the membrane, and so the strength of the battery current is made to vary from a maximum to zero, depending on the gentleness or violence of the sound. These variations of the current produce corresponding variations in the magnetism of the steel rod in the receiving apparatus, and the sounds emitted correspond to those spoken at the transmitting station.
Reis describes the operation in terms which have been held to mean that he intended to absolutely make and break the circuit at every fundamental vibration of the air, or of the membrane, and the inference has been drawn that he could not have had an instrument which would transmit speech since it cannot be transmitted in that way. To all such criticism it is sufficient to reply that there is abundant proof that he did transmit speech during his life time; that there are still living those who were with him when speech was transmitted, and lastly that his apparatus will do all that was claimed for it by him.
In the Annual Report of the Physical Society of Frankfort for 1860-61, we find a clear exposition of the problem to be accomplished, and a statement of the degree of success which it had at that time attained. It was not pretended that the instrument which he had invented and produced was fitted for commercial pur- poses, or that it would not need to be greatly improved before it could be of much practical value, yet it was claimed that the inventor had opened a new field of research and invention. Others entered the field and improvements followed both in Europe and in this country.
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In 1876, Professor A. G. Bell exhibited at the Centennial in Philadelphia, an apparatus which was capable of transmitting with more or less distinctness spoken words and sentences. Many improvements soon followed in which a great number of inventors took part, and the consequence is that the telephone has become as common as the telegraph. The plan of procedure which Prof. Bell adopted in his application for a patent differs essentially from that adopted by Reis. Instead of producing variations in a current supplied by a battery as the effective agency by which sounds are to be reproduced, he employed the energy of the sound waves to produce the current which should actuate the receiver. In short, his apparatus is merely two small magneto-engines joined up in the same circuit so that the action of the one shall compel corresponding actions in the other. We must pass without special mention the labors of Gray, McDonough, and others who have taken a conspicuous part in the development of telephony, but who have had the misfortune to be overborne by the successful monopoly secured by the American Bell Telephone Co. It will be of interest to remark that the plan of Reis has come to be the one which is now made the basis of commercial telephony. If one of the platinum pieces in his transmitter be replaced with a bit of carbon no other change need be made in his apparatus to constitute it a completely successful apparatus. The accomplishment of this is due to Edison.
The discovery of the electric are has already been mentioned as having been made by Curtet, and as having been studied by Davy. The production of the electric light for illuminating purposes was not general, however, on account of the expense attending it, until the dynamo-machine was in some good degree perfected. This as has been shown was due to the labors of several persons. Within the last decade the use of the electric light has become general in our principal cities. It is to be noticed that the inventions of electricians whereby this has been rendered possible, have, in order that they might be carried out in practice, compelled great improvements in the construction of the steam engine.
The principal facts concerning electrolysis have been mentioned on an earlier page; and the laws of Faraday concerning them have been stated. It remains to mention briefly the application which these laws have found in the arts. In 1804, Brugnatelli succeeded in gilding silver coins by means of the galvanic current. De la Rive, in 1840, covered brass and copper in the same way. In 1841, Ruolz presented to the Academy of Sciences, in Paris, a communication in which he set forth a method of practical application of electrolysis for covering conducting surfaces with metals. Large establishments at once sprung up, the most notable of which was that of Elkington Brothers, in Birmingham. The art found appli- cation in copying medals and other works of art, in the electrotyping of letter- press for the press, in copying photographs, etc. It is now applied with great success in chemical analysis, in the purification of chemical products, and in many branches of manufacture which our limits do not permit us to mention.
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HEAT.
The earliest inquiries concerning the phenomena of heat were, as in other departments, mostly speculative in their character. It was one of the " elemen- tary opposites " of Anaximander. According to him all things were formed by combinations of the hot and the cold, the dry and the moist. Others regarded heat as a form of creative power, if not the creative power itself. The sun being its most striking manifestation naturally came to be regarded as a proper object of worship. Democritus regarded heat as as efflux of exceedingly minute round particles, which could move with great velocity so as to penetrate all substances. From the finest of these particles the soul was constituted. Aristotle taught that heat is a condition of matter rather than matter itself. Bacon conceived it to consist in the motion of the minute particles of which all bodies are composed. Locke held similar views. Stahl, born 1660, developed an idea of Becher, that "phlogiston " is the principle of heat. This notion was intimately connected with the chemistry, or rather the alchemy, of the times in which they lived. The metals were combinations of certain calces (rusts) with phlogiston; and as this latter had the inherent property of levity, it was easy to explain the fact, that when a certain amount of calx was heated with charcoal, which was supposed to be mostly composed of phlogiston, it weighed less than the calx did before heat- ing. The phlogiston entered into combination with the calx to constitute the metal, and so made the whole lighter. When, however, oxygen gas was dis- covered by Steele, in 1774, it became possible to show the fallacy of this assump- tion and the unreality of phlogiston. Then the " caloric " theory came forward, being powerfully advocated by Lavoisier and Black. It assumed that heat is a real substance capable of entering into conibination with other substances, and of passing from one body to another. This hypothesis could be overthrown only by showing that heat can be produced without recourse to any source of pre-exist- ing heat. This was done by Count Rumford, 1796-98. He found that the heat developed during the boring of cannon which he was engaged in constructing, was greater than could be accounted for by the changes in the form and density of the materials concerned. Sir Humphry Davy shortly after confirmed this con- clusion by causing ice to melt by means of friction, in a vacuum and in a room the temperature of which was below the freezing point. Finally Joule, 1843-50, fully proved that heat and mechanical energy are mutually convertible and ascer- tained, with great accuracy, the ." mechanical equivalent " of a unit of heat. The general result may be stated thus: A pound of water is heated one degree F. by the expenditure of an amount of mechanical energy which would raise 772 lbs. one foot.
The conclusion of Joule has been confirmed, with very slight corrections, by others and by experiments widely differing in their character and mode of attack.
There are two distinct lines of inquiry to be reviewed which will exhibit the
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progress which has been made during the century just past. One of these has to do with the laws of distribution and the effects of heat in altering the properties of bodies, and the other is concerned with heat considered as source of energy for accomplishing work in the mechanical sense.
The progress of knowledge in this, as in every other, branch of physical science has been inseparably connected with the invention of the necessary ins- truments of observation. As respects heat, the most important as well as the earliest of these is the thermometer. The instrument is based on the almost universal effect of heat in increasing the bulk of bodies to which it is applied.
The inventor of the thermometer appears to have been Galileo, about 1592, though there are not wanting some evidences that attempts were made by others, about the same time, to measure the temperature of bodies. The thermometer of Galileo was simply a glass tube on the end of which was blown a bulb, the open end of the tube being dipped below the surface of water in a vessel. When the bulb was heated gently a portion of the air was driven out by expansion, and on cooling, the water rose in the tube and by its height showed the temperature to which the bulb had been exposed. The defect of this instrument, besides the inconvenience of its application, was that it was affected by changes in the pres- sure of the atmosphere. About fifty years later Guericke improved this form of apparatus by employing a large copper bulb with a siphon shaped tube attached in a vertical position, and partly filled with alcohol. A small float rested on the upper surface of the alcohol and had a string attached to its upper surface so that it, passing over a pulley, could cause a small figure to traverse up and down over a scale, as the temperature varied. He assumed the temperature at which the first hoar-frost appeared as the mean temperature of his scale. By means of his air-pump he withdrew through a small tube which could be closed, so much air as was required to make the position of the figure coincide with the assumed point on the scale. The instrument, of course was subject to the same disadvan- tages as that of Galileo. The Florentine Academicians were the first to employ a real thermometer in which the effects of atmospheric pressure were excluded. It was probably invented by Friedrich II, Grand Duke of Toscany. The tube contained alcohol, and was pumped out so as to enclose a vacuum and then it was hermetically sealed. The instrument was in existence in 1641, even before the founding of the Academy.
In 1703, Amontons presented a memoir to the Paris Academy in which he showed that the temperature indicated by an open-air thermometer, was propor- tional to the elasticity of the enclosed air; and he pointed out that by reference to the barometer, the varying effects of atmospheric pressure could be elimi- nated. He knew the fact that water boils at a constant temperature, and for the first time he made use of this fact for fixing one of the points of his thermome- ter scale. He discovered and stated two important laws: " A given quantity of air increases in elasticity proportionally with the increase of heat which it re-
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ceives. A given quantity of air, at a constant temperature, increases in elastici- ty proportionally with the increase of pressure which it experiences."
The first form of thermometer which made Fahrenheit famous, was filled with alcohol. Instruments of his construction were common in Europe as early as 1709. About 1714-15, he employed mercury for filling the instrument. In 1724, he published his method of procedure in finding the points of reference for his scales. He took the temperature produced by a mixture of ice, water and salt, for zero. The temperature of a mixture of ice and water he marked 32; that of the human mouth he marked 96. The thermometers of Reaumer and Celsius, differ in no respect from that of Fahrenheit, save in the value of the degrees of their scales. Mention has been made of the thermo-pile under the head of elec- tricity.
The thermometer as constructed of glass and filled with mercury or any other known liquid, is far from being a strictly accurate instrument, if it be used on the assumption that throughout the whole extent of its scale, equal degrees cor- respond to equal amounts of heat. Accordingly, laborious researches have been undertaken to ascertain the laws which regulate the expansion of mercury and other liquids, as well as those which apply to the expansion of solids. The most notable of these labors as well as the most accurate, are those of Regnault, un- dertaken in order to determine the data necessary for calculating the duty, effi- ciency, etc., of the steam engine. His results were submitted in 1847. They are of the utmost importance to science, but are too complicated to be presented here.
The expansion of gases had been studied by several philosophers. Amontons, 1699; Hawksbee, 1708; Lambert, 1779; and especially by Gay Lussac, when Regnault undertook the investigation with the rigor and completeness which characterizes all his work. He was the first to show that the latent heat of steam diminishes as the sensible heat increases, though not in the same ratio. In general, he confirmed the law of Boyle, that the volume of a gas is in the inverse ratio of the pressure to which it is subjected, the temperature remaining constant.
The term temperature stands for an idea wholly differing from that involved in the expression quantity of heat. It is clear that a small amount of water, for instance, may be heated to a given temperature with a less expenditure of fuel than would be required to heat a larger amount to the same temperature, yet the thermometer would give the same indication when placed in the one as when placed in the other. The branch of science which relates to the measurement of quantities of heat is called calorimetry. It had its origin with Deluc. In the winter of 1754-55, he allowed the water surrounding a thermometer in a glass to freeze. On carrying the glass to the fire he noticed that the thermometer indi- cated a rise in temperature only till the ice began to melt. From that time on, the mercury remained at the zero point until the ice had entirely melted. Black
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about the same time studied the same phenomenon, and he found that when he mixed ice at 32 degrees F. with water at 172, he did not have a mean of these two temperatures, but that the whole showed a temperature of 32, and the ice was changed into water. He concluded that a large quantity of heat passed from the water into the ice and became hidden in changing it into water so that the ther- mometer could not take cognizance of it. He called this heat "latent heat." Black's researches were published in 1779, by Crawford. Reichmann, in St. Petersburg, found that the temperature obtained when quantities of the same liquids, un- equally heated, are mixed is the mean of their temperatures, reference being had to the quantity of each in the mixture. Wilke, in 1772, found, on mixing ice-cold water with water of a higher temperature, that Reichmann's law was confirmed. On taking equal quantities of water and of snow at the melting point, he found that, on mixing them, 72 degrees C. disappeared entirely, or be- came latent. He was then led to inquire whether different bodies required different amounts of heat to raise their temperature to the same degree, other things being equal. To this end, he heated the body under examination and plunged it into the ice-cold water, and noted how much its temperature was raised. Of course the mass of the body, as well as that of the water, was ascer- tained, in order to the necessary calculations. After the work of Wilke, inqui- ries respecting the specific heat of different bodies became frequent, and the value of such researches was fully recognized. It may be well here to give a sharp definition of " specific heat" that the reader may more fully appreciate the importance of the subject. The quantity of heat required to raise one unit mass (say kilogramme or pound) of a substance from zero to one degree, is its specific heat. It requires thirty times as much heat to raise the temperature of a quantity of water one degree as it does to raise the temperature of the same weight of mercury by the same amount, for example.
This great capacity of water for heat makes it admirably fitted to play the part of a regulator of climate. It stores up heat in the warmer seasons of the year to be given out during the colder. So, too, the Gulf Stream, having its origin in the warm latitudes, conveys to the higher latitudes immense quantities of heat, which there become efficient in softening their rigor.
It is evident that there are sources of error in this method of mixture, which must be carefully guarded against. The vessel in which the mixture is made will have its temperature altered, and besides, it will be losing heat during the time of the necessary observations, by radiation. Careful treatment can, for the greater part, eliminate these. It was natural that other plans of procedure should be devised in order to confirm and correct, if need be, the determinations made by the method of mixtures. In 1777, Lavoisier and Laplace invented an ice calorimeter, by means of which they could find the specific heat of bodies by reference to the amounts of ice they could melt when raised to a given tem- perature. The facts brought to light by all these inquiries, and the means used
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to secure them, raised anew the old controversies concerning the nature of heat. The vibratory theory was opposed by the theory which regards heat as a peculiar substance. And here, no doubt, as in other cases, the great authority of Newton did much to influence the opinions of the contestants. He had taught that light is composed of exceedingly minute particles thrown off from the luminous body with great velocity. Why should not heat be material also ? Wilke held that it is, and that its particles are self-repellant, but are attracted by most other forms of matter. Every body has its own proper amount of this heat mat- ter, but when the condition of a body is altered the amount of heat it can contain is correspondingly changed. This view enabled him to offer plausible explanations of observed facts which had thitherto proved enigmas; for exam- ple, the changes in temperature of air when it is made to expand and when it is compressed. The theory of phlogiston, which was reigning in the contempo- raneous chemistry, was closely akin to this material hypothesis concerning heat; indeed, in some aspects, it was identical with it, as may be inferred from re- marks on an earlier page.
The determination of the specific heat of gases is a difficult problem, but one of the greatest theoretical importance. In fact, there are two specific heats to be determined for every gas. Since the expansion or the contraction of a gas is accompanied by a change of temperature, it is clear that the specific heat of a gas, if determined while the gas is so confined that its volume cannot alter, will differ from the specific heat when determined under conditions which permit changes in volume corresponding with the changes in temperature. The ratio of one of these specific heats to the other is a different number for every different gas, and is closely related to molecular structure. In calculating the velocity of the transmission of sound through any given gas, this ratio is an important fac- tor. It is, hence, possible to determine this ratio independently of calorimetric methods by means of observations on the velocity of sound through any given gas. In Newton's time, knowledge of the relations here considered were want- ing, and for this reason he failed to make his calculated velocity of sound in air agree with the observed velocity. Laplace pointed out the reason for the disa- greement.
Without delaying to mention details, it may be remarked in passing that the whole matter of the distribution of heat has been fully treated by the mathema- ticians, and notably by Fourier, who, between the years 1807 and 1820, commu- nicated to the Institute of France a complete analytical treatment of the problem involved. A very important law, established by Dulong and Petit, should be mentioned: The same amount of heat is required to raise an atom of any simple substance to a given temperature as is required to raise an atom of any other simple substance by the same amount. In other words, the product of the spe- cific heat and the atomic weight, for any simple body, is a constant quantity. Regnault has shown that this law may be extended to compound substances hav-
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ing the same composition. This law has an important theoretical bearing upon the views which we must hold concerning the constitution of matter. Many in- teresting relations of heat to changes in the form of matter must be passed by. The kinetic theory of gases is, however, too important to be left unmen- tioned. It is well known that any gas, if free to do so, will expand and fill any available space. This property was formerly attributed to the repulsive action of heat, with which the molecules were supposed to be charged, or united. The kinetic theory assumes that the least particles of a free gas are minute, perfectly (in a perfect gas) elastic solids, which are constantly moving with great velocity. Their paths are right lines, except when one particle encounters another, or the wall of the containing vessel. The aggregate of the blows struck by the moving particles constitutes the pressure which a gas can exert when confined. In the case of the atmosphere in which we move, the average pressure of 15 lbs. to the square inch is due to the united blows struck by the air particles per square inch of surface. When a confined gas is heated, this pressure increases. The kinetic theory asserts that this is due to the greater velocity of the particles. If, in the heated state, they were allowed to expand, they would at once assume a longer free path, and thus the expansion is explained. It is possible to calculate what is the mean average velocity of the particle, on the supposition that the kinetic theory is true, and the calculation is found to be consistent with the results of experiment. There are abundant reasons, which cannot be presented here, for the belief that the kinetic theory, thus briefly and imperfectly noticed, is correct.
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