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FRANKLIN'S THEORY OF ELECTRICITY According to Franklin's theory, electricity exists in all bodies as a "common stock," and tends to seek and remain in a state of equilibrium, just as fluids naturally tend to seek a level. But it may, nevertheless, be raised or lowered, and this equilibrium be thus disturbed. If a body has more electricity than its normal amount it is said to be POSITIVELY electrified; but if it has less, it is NEGATIVELY electrified. An over-electrified or "plus" body tends to give its surplus stock to a body containing the normal amount; while the "minus" or under-electrified body will draw electricity from one containing the normal amount. Working along lines suggested by this theory, Franklin attempted to show that electricity is not created by friction, but simply collected from its diversified state, the rubbed glass globe attracting a certain quantity of "electrical fire," but ever ready to give it up to any body that has less. He explained the charged Leyden jar by showing that the inner coating of tin-foil received more than the ordinary quantity of electricity, and in consequence is POSITIVELY electrified, while the outer coating, having the ordinary quantity of electricity diminished, is electrified NEGATIVELY. These studies of the Leyden jar, and the studies of pieces of glass coated with sheet metal, led Franklin to invent his battery, constructed of eleven large glass plates coated with sheets of lead. With this machine, after overcoming some defects, he was able to produce electrical manifestations of great force--a force that "knew no bounds," as he declared ("except in the matter of expense and of labor"), and which could be made to exceed "the greatest know effects of common lightning." This reference to lightning would seem to show Franklin's belief, even at that time, that lightning is electricity. Many eminent observers, such as Hauksbee, Wall, Gray, and Nollet, had noticed the resemblance between electric sparks and lightning, but none of these had more than surmised that the two might be identical. In 1746, the surgeon, John Freke, also asserted his belief in this identity. Winkler, shortly after this time, expressed the same belief, and, assuming that they were the same, declared that "there is no proof that they are of different natures"; and still he did not prove that they were the same nature.

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FRANKLIN INVENTS THE LIGHTNING-ROD Even before Franklin proved conclusively the nature of lightning, his experiments in drawing off the electric charge with points led to some practical suggestions which resulted in the invention of the lightning-rod. In the letter of July, 1750, which he wrote on the subject, he gave careful instructions as to the way in which these rods might be constructed. In part Franklin wrote: "May not the knowledge of this power of points be of use to mankind in preserving houses, churches, ships, etc., from the stroke of lightning by directing us to fix on the highest parts of the edifices upright rods of iron made sharp as a needle, and gilt to prevent rusting, and from the foot of these rods a wire down the outside of the building into the grounds, or down round one of the shrouds of a ship and down her side till it reaches the water? Would not these pointed rods probably draw the electrical fire silently out of a cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible mischief? "To determine this question, whether the clouds that contain the lightning are electrified or not, I propose an experiment to be tried where it may be done conveniently. On the top of some high tower or steeple, place a kind of sentry-box, big enough to contain a man and an electrical stand. From the middle of the stand let an iron rod rise and pass, bending out of the door, and then upright twenty or thirty feet, pointed very sharp at the end. If the electrical stand be kept clean and dry, a man standing on it when such clouds are passing low might be electrified and afford sparks, the rod drawing fire to him from a cloud. If any danger to the man be apprehended (though I think there would be none), let him stand on the floor of his box and now and then bring near to the rod the loop of a wire that has one end fastened to the leads, he holding it by a wax handle; so the sparks, if the rod is electrified, will strike from the rod to the wire and not effect him."[4] Not satisfied with all the evidence that he had collected pointing to the identity of lightning and electricity, he adds one more striking and very suggestive piece of evidence. Lightning was known sometimes to strike persons blind without killing them. In experimenting on pigeons and pullets with his electrical machine, Franklin found that a fowl, when not killed outright, was sometimes rendered blind. The report of these experiments were incorporated in this famous letter of the Philadelphia philosopher. The attitude of the Royal Society towards this clearly stated letter, with its useful suggestions, must always remain as a blot on the record of this usually very receptive and liberal-minded body. Far from publishing it or receiving it at all, they derided the whole matter as too visionary for discussion by the society. How was it possible that any great scientific discovery could be made by a self-educated colonial newspaper editor, who knew nothing of European science except by hearsay, when all the great scientific minds of Europe had failed to make the discovery? How indeed! And yet it would seem that if any of the influential members of the learned society had taken the trouble to read over Franklin's clearly stated letter, they could hardly have failed to see that his suggestions were worthy of consideration. But at all events, whether they did or did not matters little. The fact remains that they refused to consider the paper seriously at the time; and later on, when its true value became known, were obliged to acknowledge their error by a tardy report on the already well-known document. But if English scientists were cold in their reception of Franklin's theory and suggestions, the French scientists were not. Buffon, perceiving at once the importance of some of Franklin's experiments, took steps to have the famous letter translated into French, and soon not only the savants, but members of the court and the king himself were intensely interested. Two scientists, De Lor and D'Alibard, undertook to test the truth of Franklin's suggestions as to pointed rods "drawing off lightning." In a garden near Paris, the latter erected a pointed iron rod fifty feet high and an inch in diameter. As no thunder-clouds appeared for several days, a guard was stationed, armed with an insulated brass wire, who was directed to test the iron rods with it in case a storm came on during D'Alibard's absence. The storm did come on, and the guard, not waiting for his employer's arrival, seized the wire and touched the rod. Instantly there was a report. Sparks flew and the guard received such a shock that he thought his time had come. Believing from his outcry that he was mortally hurt, his friends rushed for a spiritual adviser, who came running through rain and hail to administer the last rites; but when he found the guard still alive and uninjured, he turned his visit to account by testing the rod himself several times, and later writing a report of his experiments to M. d'Alibard. This scientist at once reported the affair to the French Academy, remarking that "Franklin's idea was no longer a conjecture, but a reality."

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FRANKLIN PROVES THAT LIGHTNING IS ELECTRICITY Europe, hitherto somewhat sceptical of Franklin's views, was by this time convinced of the identity of lightning and electricity. It was now Franklin's turn to be sceptical. To him the fact that a rod, one hundred feet high, became electrified during a storm did not necessarily prove that the storm-clouds were electrified. A rod of that length was not really projected into the cloud, for even a very low thunder-cloud was more than a hundred feet above the ground. Irrefutable proof could only be had, as he saw it, by "extracting" the lightning with something actually sent up into the storm-cloud; and to accomplish this Franklin made his silk kite, with which he finally demonstrated to his own and the world's satisfaction that his theory was correct. Taking his kite out into an open common on the approach of a thunder-storm, he flew it well up into the threatening clouds, and then, touching, the suspended key with his knuckle, received the electric spark; and a little later he charged a Leyden jar from the electricity drawn from the clouds with his kite. In a brief but direct letter, he sent an account of his kite and his experiment to England: "Make a small cross of two light strips of cedar," he wrote, "the arms so long as to reach to the four corners of a large, thin, silk handkerchief when extended; tie the corners of the handkerchief to the extremities of the cross so you have the body of a kite; which being properly accommodated with a tail, loop, and string, will rise in the air like those made of paper; but this being of silk is fitter to bear the wind and wet of a thunder-gust without tearing. To the top of the upright stick of the cross is to be fixed a very sharp-pointed wire, rising a foot or more above the wood. To the end of the twine, next the hand, is to be tied a silk ribbon; where the silk and twine join a key may be fastened. This kite is to be raised when a thunder-gust appears to be coming on, and the person who holds the string must stand within a door or window or under some cover, so that the silk ribbon may not be wet; and care must be taken that the twine does not touch the frame of the door or window. As soon as any of the thunder-clouds come over the kite, the pointed wire will draw the electric fire from them, and the kite, with all the twine, will be electrified and the loose filaments will stand out everywhere and be attracted by the approaching finger, and when the rain has wet the kite and twine so that it can conduct the electric fire freely, you will find it stream out plentifully from the key on the approach of your knuckle, and with this key the phial may be charged; and from electric fire thus obtained spirits may be kindled and all other electric experiments performed which are usually done by the help of a rubbed glass globe or tube, and thereby the sameness of the electric matter with that of lightning completely demonstrated."[5] In experimenting with lightning and Franklin's pointed rods in Europe, several scientists received severe shocks, in one case with a fatal result. Professor Richman, of St. Petersburg, while experimenting during a thunder-storm, with an iron rod which he had erected on his house, received a shock that killed him instantly. About 1733, as we have seen, Dufay had demonstrated that there were two apparently different kinds of electricity; one called VITREOUS because produced by rubbing glass, and the other RESINOUS because produced by rubbed resinous bodies. Dufay supposed that these two apparently different electricities could only be produced by their respective substances; but twenty years later, John Canton (1715-1772), an Englishman, demonstrated that under certain conditions both might be produced by rubbing the same substance. Canton's experiment, made upon a glass tube with a roughened surface, proved that if the surface of the tube were rubbed with oiled silk, vitreous or positive electricity was produced, but if rubbed with flannel, resinous electricity was produced. He discovered still further that both kinds could be excited on the same tube simultaneously with a single rubber. To demonstrate this he used a tube, one-half of which had a roughened the other a glazed surface. With a single stroke of the rubber he was able to excite both kinds of electricity on this tube. He found also that certain substances, such as glass and amber, were electrified positively when taken out of mercury, and this led to his important discovery that an amalgam of mercury and tin, when used on the surface of the rubber, was very effective in exciting glass.

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XV. NATURAL HISTORY TO THE TIME OF LINNAeUS Modern systematic botany and zoology are usually held to have their beginnings with Linnaeus. But there were certain precursors of the famous Swedish naturalist, some of them antedating him by more than a century, whose work must not be altogether ignored--such men as Konrad Gesner (1516-1565), Andreas Caesalpinus (1579-1603), Francisco Redi (1618-1676), Giovanni Alfonso Borelli (1608-1679), John Ray (1628-1705), Robert Hooke (1635-1703), John Swammerdam (1637-1680), Marcello Malpighi (1628-1694), Nehemiah Grew (1628-1711), Joseph Tournefort (1656-1708), Rudolf Jacob Camerarius (1665-1721), and Stephen Hales (1677-1761). The last named of these was, to be sure, a contemporary of Linnaeus himself, but Gesner and Caesalpinus belong, it will be observed, to so remote an epoch as that of Copernicus. Reference has been made in an earlier chapter to the microscopic investigations of Marcello Malpighi, who, as there related, was the first observer who actually saw blood corpuscles pass through the capillaries. Another feat of this earliest of great microscopists was to dissect muscular tissue, and thus become the father of microscopic anatomy. But Malpighi did not confine his observations to animal tissues. He dissected plants as well, and he is almost as fully entitled to be called the father of vegetable anatomy, though here his honors are shared by the Englishman Grew. In 1681, while Malpighi's work, Anatomia plantarum, was on its way to the Royal Society for publication, Grew's Anatomy of Vegetables was in the hands of the publishers, making its appearance a few months earlier than the work of the great Italian. Grew's book was epoch-marking in pointing out the sex-differences in plants. Robert Hooke developed the microscope, and took the first steps towards studying vegetable anatomy, publishing in 1667, among other results, the discovery of the cellular structure of cork. Hooke applied the name "cell" for the first time in this connection. These discoveries of Hooke, Malpighi, and Grew, and the discovery of the circulation of the blood by William Harvey shortly before, had called attention to the similarity of animal and vegetable structures. Hales made a series of investigations upon animals to determine the force of the blood pressure; and similarly he made numerous statical experiments to determine the pressure of the flow of sap in vegetables. His Vegetable Statics, published in 1727, was the first important work on the subject of vegetable physiology, and for this reason Hales has been called the father of this branch of science. In botany, as well as in zoology, the classifications of Linnaeus of course supplanted all preceding classifications, for the obvious reason that they were much more satisfactory; but his work was a culmination of many similar and more or less satisfactory attempts of his predecessors. About the year 1670 Dr. Robert Morison (1620-1683), of Aberdeen, published a classification of plants, his system taking into account the woody or herbaceous structure, as well as the flowers and fruit. This classification was supplanted twelve years later by the classification of Ray, who arranged all known vegetables into thirty-three classes, the basis of this classification being the fruit. A few years later Rivinus, a professor of botany in the University of Leipzig, made still another classification, determining the distinguishing character chiefly from the flower, and Camerarius and Tournefort also made elaborate classifications. On the Continent Tournefort's classification was the most popular until the time of Linnaeus, his systematic arrangement including about eight thousand species of plants, arranged chiefly according to the form of the corolla. Most of these early workers gave attention to both vegetable and animal kingdoms. They were called naturalists, and the field of their investigations was spoken of as "natural history." The specialization of knowledge had not reached that later stage in which botanist, zoologist, and physiologist felt their labors to be sharply divided. Such a division was becoming more and more necessary as the field of knowledge extended; but it did not become imperative until long after the time of Linnaeus. That naturalist himself, as we shall see, was equally distinguished as botanist and as zoologist. His great task of organizing knowledge was applied to the entire range of living things. Carolus Linnaeus was born in the town of Rashult, in Sweden, on May 13, 1707. As a child he showed great aptitude in learning botanical names, and remembering facts about various plants as told him by his father. His eagerness for knowledge did not extend to the ordinary primary studies, however, and, aside from the single exception of the study of physiology, he proved himself an indifferent pupil. His backwardness was a sore trial to his father, who was desirous that his son should enter the ministry; but as the young Linnaeus showed no liking for that calling, and as he had acquitted himself well in his study of physiology, his father at last decided to allow him to take up the study of medicine. Here at last was a field more to the liking of the boy, who soon vied with the best of his fellow-students for first honors. Meanwhile he kept steadily at work in his study of natural history, acquiring considerable knowledge of ornithology, entomology, and botany, and adding continually to his collection of botanical specimens. In 1729 his botanical knowledge was brought to the attention of Olaf Rudbeck, professor of botany in the University of Upsala, by a short paper on the sexes of plants which Linnaeus had prepared. Rudbeck was so impressed by some of the ideas expressed in this paper that he appointed the author as his assistant the following year. This was the beginning of Linnaes's career as a botanist. The academic gardens were thus thrown open to him, and he found time at his disposal for pursuing his studies between lecture hours and in the evenings. It was at this time that he began the preparation of his work the Systema naturae, the first of his great works, containing a comprehensive sketch of the whole field of natural history. When this work was published, the clearness of the views expressed and the systematic arrangement of the various classifications excited great astonishment and admiration, and placed Linaeus at once in the foremost rank of naturalists. This work was followed shortly by other publications, mostly on botanical subjects, in which, among other things, he worked out in detail his famous "system." This system is founded on the sexes of plants, and is usually referred to as an "artificial method" of classification because it takes into account only a few marked characters of plants, without uniting them by more general natural affinities. At the present time it is considered only as a stepping-stone to the "natural" system; but at the time of its promulgation it was epoch-marking in its directness and simplicity, and therefore superiority, over any existing systems. One of the great reforms effected by Linnaeus was in the matter of scientific terminology. Technical terms are absolutely necessary to scientific progress, and particularly so in botany, where obscurity, ambiguity, or prolixity in descriptions are fatally misleading. Linnaeus's work contains something like a thousand terms, whose meanings and uses are carefully explained. Such an array seems at first glance arbitrary and unnecessary, but the fact that it has remained in use for something like two centuries is indisputable evidence of its practicality. The descriptive language of botany, as employed by Linnaeus, still stands as a model for all other subjects. Closely allied to botanical terminology is the subject of botanical nomenclature. The old method of using a number of Latin words to describe each different plant is obviously too cumbersome, and several attempts had been made prior to the time of Linnaeus to substitute simpler methods. Linnaeus himself made several unsatisfactory attempts before he finally hit upon his system of "trivial names," which was developed in his Species plantarum, and which, with some, minor alterations, remains in use to this day. The essence of the system is the introduction of binomial nomenclature--that is to say, the use of two names and no more to designate any single species of animal or plant. The principle is quite the same as that according to which in modern society a man has two names, let us say, John Doe, the one designating his family, the other being individual. Similarly each species of animal or plant, according to the Linnaeean system, received a specific or "trivial" name; while various species, associated according to their seeming natural affinities into groups called genera, were given the same generic name. Thus the generic name given all members of the cat tribe being Felis, the name Felis leo designates the lion; Felis pardus, the leopard; Felis domestica, the house cat, and so on. This seems perfectly simple and natural now, but to understand how great a reform the binomial nomenclature introduced we have but to consult the work of Linnaeus's predecessors. A single illustration will suffice. There is, for example, a kind of grass, in referring to which the naturalist anterior to Linnaeus, if he would be absolutely unambiguous, was obliged to use the following descriptive formula: Gramen Xerampelino, Miliacea, praetenuis ramosaque sparsa panicula, sive Xerampelino congener, arvense, aestivum; gramen minutissimo semine. Linnaeus gave to this plant the name Poa bulbosa--a name that sufficed, according to the new system, to distinguish this from every other species of vegetable. It does not require any special knowledge to appreciate the advantage of such a simplification. While visiting Paris in 1738 Linnaeus met and botanized with the two botanists whose "natural method" of classification was later to supplant his own "artificial system." These were Bernard and Antoine Laurent de Jussieu. The efforts of these two scientists were directed towards obtaining a system which should aim at clearness, simplicity, and precision, and at the same time be governed by the natural affinities of plants. The natural system, as finally propounded by them, is based on the number of cotyledons, the structure of the seed, and the insertion of the stamens. Succeeding writers on botany have made various modifications of this system, but nevertheless it stands as the foundation-stone of modern botanical classification.

APPENDIX REFERENCE LIST CHAPTER I SCIENCE IN THE DARK AGE [1] (p. 4). James Harvey Robinson, An Introduction to the History of Western Europe, New York, 1898, p. 330. [2] (p. 6). Henry Smith Williams, A Prefatory Characterization of The History of Italy, in vol. IX. of The Historians' History of the World, 25 vols., London and New York, 1904.

CHAPTER III MEDIAeVAL SCIENCE IN THE WEST [1] (p. 47). Etigene Muntz, Leonardo do Vinci, Artist, Thinker, and Man of Science, 2 vols., New York, 1892. Vol. II., p. 73.

CHAPTER IV THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO [1] (p. 62). Copernicus, uber die Kreisbewegungen der Welfkorper, trans. from Dannemann's Geschichle du Naturwissenschaften, 2 vols., Leipzig, 1896. [2] (p. 90). Galileo, Dialogo dei due Massimi Systemi del Mondo, trans. from Dannemann, op. cit. CHAPTER V GALILEO AND THE NEW PHYSICS [1] (p. 101). Rothmann, History of Astronomy (in the Library of Useful Knowledge), London, 1834. [2] (p. 102). William Whewell, History of the Inductive Sciences, 3 Vols, London, 1847-Vol. II., p. 48. [3] (p. 111). The Lives of Eminent Persons, by Biot, Jardine, Bethune, etc., London, 1833. [4] (p. 113). William Gilbert, De Magnete, translated by P. Fleury Motteley, London, 1893. In the biographical memoir, p. xvi. [5] (p. 114). Gilbert, op. cit., p. x1vii. [6] (p. 114). Gilbert, op. cit., p. 24.

CHAPTER VI TWO PSEUDO-SCIENCES--ALCHEMY AND ASTROLOGY [1] (p. 125). Exodus xxxii, 20. [2] (p. 126). Charles Mackay, Popular Delusions, 3 vols., London, 1850. Vol. II., p. 280. [3] (p. 140). Mackay, op. cit., Vol. 11., p. 289. [4] (P. 145). John B. Schmalz, Astrology Vindicated, New York, 1898. [5] (p. 146). William Lilly, The Starry Messenger, London, 1645, p. 63. [6] (p. 149). Lilly, op. cit., p. 70. [7] (p. 152). George Wharton, An Astrological jugement upon His Majesty's Present March begun from Oxford, May 7, 1645, pp. 7-10. [8] (p. 154). C. W. Roback, The Mysteries of Astrology, Boston, 1854, p. 29.