a history of science-2-第49部分
按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
r discoveries。 Musschenbroek was one of the foremost teachers of Europe； and so widely known that the great universities vied with each other； and kings were bidding； for his services。 Naturally； any discovery made by such a famous person would soon be heralded from one end of Europe to the other。 And so when this professor of Leyden made his discovery； the apparatus came to be called the 〃Leyden jar；〃 for want of a better name。 There can be little doubt that Musschenbroek made his discovery entirely independently of any knowledge of Von Kleist's； or； for that matter； without ever having heard of the Pomeranian； and his actions in the matter are entirely honorable。 His discovery was the result of an accident。 While experimenting to determine the strength of electricity he suspended a gun…barrel； which he charged with electricity from a revolving glass globe。 From the end of the gun…barrel opposite the globe was a brass wire； which extended into a glass jar partly filled with water。 Musschenbroek held in one hand this jar； while with the other he attempted to draw sparks from the barrel。 Suddenly he received a shock in the hand holding the jar； that 〃shook him like a stroke of lightning；〃 and for a moment made him believe that 〃he was done for。〃 Continuing his experiments； nevertheless； he found that if the jar were placed on a piece of metal on the table； a shock would be received by touching this piece of metal with one hand and touching the wire with the otherthat is； a path was made for the electrical discharge through the body。 This was practically the same experiment as made by Von Kleist with his bottle and nail； but carried one step farther； as it showed that the 〃jar〃 need not necessarily be held in the hand； as believed by Von Kleist。 Further experiments； continued by many philosophers at the time； revealed what Von Kleist had already pointed out； that the electrified jar remained charged for some time。 Soon after this Daniel Gralath； wishing to obtain stronger discharges than could be had from a single Leyden jar； conceived the idea of combining several jars； thus for the first time grouping the generators in a 〃battery〃 which produced a discharge strong enough to kill birds and small animals。 He also attempted to measure the strength of the discharges； but soon gave it up in despair； and the solution of this problem was left for late nineteenth…century scientists。 The advent of the Leyden jar； which made it possible to produce strong electrical discharges from a small and comparatively simple device； was followed by more spectacular demonstrations of various kinds all over Europe。 These exhibitions aroused the interest of the kings and noblemen； so that electricity no longer remained a 〃plaything of the philosophers〃 alone； but of kings as well。 A favorite demonstration was that of sending the electrical discharge through long lines of soldiers linked together by pieces of wire； the discharge causing them to 〃spring into the air simultaneously〃 in a most astonishing manner。 A certain monk in Paris prepared a most elaborate series of demonstrations for the amusement of the king； among other things linking together an entire regiment of nine hundred men； causing them to perform simultaneous springs and contortions in a manner most amusing to the royal guests。 But not all the experiments being made were of a purely spectacular character； although most of them accomplished little except in a negative way。 The famous Abbe Nollet； for example； combined useful experiments with spectacular demonstrations； thus keeping up popular interest while aiding the cause of scientific electricity。
WILLIAM WATSON Naturally； the new discoveries made necessary a new nomenclature； new words and electrical terms being constantly employed by the various writers of that day。 Among these writers was the English scientist William Watson； who was not only a most prolific writer but a tireless investigator。 Many of the words coined by him are now obsolete； but one at least； 〃circuit；〃 still remains in use。 In 1746； a French scientist； Louis Guillaume le Monnier； bad made a circuit including metal and water by laying a chain half…way around the edge of a pond； a man at either end holding it。 One of these men dipped his free hand in the water； the other presenting a Leyden jar to a rod suspended on a cork float on the water； both men receiving a shock simultaneously。 Watson； a year later； attempted the same experiment on a larger scale。 He laid a wire about twelve hundred feet long across Westminster Bridge over the Thames； bringing the ends to the water's edge on the opposite banks； a man at one end holding the wire and touching the water。 A second man on the opposite side held the wire and a Leyden jar； and a third touched the jar with one hand； while with the other he grasped a wire that extended into the river。 In this way they not only received the shock； but fired alcohol as readily across the stream as could be done in the laboratory。 In this experiment Watson discovered the superiority of wire over chain as a conductor； rightly ascribing this superiority to the continuity of the metal。 Watson continued making similar experiments over longer watercourses； some of them as long as eight thousand feet； and while engaged in making one of these he made the discovery so essential to later inventions； that the earth could be used as part of the circuit in the same manner as bodies of water。 Lengthening his wires he continued his experiments until a circuit of four miles was made； and still the electricity seemed to traverse the course instantaneously； and with apparently undiminished force； if the insulation was perfect。
BENJAMIN FRANKLIN Watson's writings now carried the field of active discovery across the Atlantic； and for the first time an American scientist appeareda scientist who not only rivalled； but excelled； his European contemporaries。 Benjamin Franklin； of Philadelphia； coming into possession of some of Watson's books； became so interested in the experiments described in them that he began at once experimenting with electricity。 In Watson's book were given directions for making various experiments； and these assisted Franklin in repeating the old experiments； and eventually adding new ones。 Associated with Franklin； and equally interested and enthusiastic； if not equally successful in making discoveries； were three other men； Thomas Hopkinson； Philip Sing； and Ebenezer Kinnersley。 These men worked together constantly； although it appears to have been Franklin who made independently the important discoveries； and formulated the famous Franklinian theory。 Working steadily； and keeping constantly in touch with the progress of the European investigators； Franklin soon made some experiments which he thought demonstrated some hitherto unknown phases of electrical manifestation。 This was the effect of pointed bodies 〃in DRAWING OFF and THROWING OFF the electrical fire。〃 In his description of this phenomenon； Franklin writes： 〃Place an iron shot of three or four inches diameter on the mouth of a clean； dry； glass bottle。 By a fine silken thread from the ceiling right over the mouth of the bottle； suspend a small cork ball； about the bigness of a marble； the thread of such a length that the cork ball may rest against the side of the shot。 Electrify the shot； and the ball will be repelled to the distance of four or five inches； more or less； according to the quantity of electricity。 When in this state； if you present to the shot the point of a long； slender shaft…bodkin； at six or eight inches distance； the repellency is instantly destroyed； and the cork flies to the shot。 A blunt body must be brought within an inch； and draw a spark； to produce the same effect。 〃To prove that the electrical fire is DRAWN OFF by the point； if you take the blade of the bodkin out of the wooden handle and fix it in a stick of sealing…wax； and then present it at the distance aforesaid； or if you bring it very near； no such effect follows； but sliding one finger along the wax till you touch the blade； and the ball flies to the shot immediately。 If you present the point in the dark you will see； sometimes at a foot distance； and more； a light gather upon it like that of a fire…fly or glow…worm； the less sharp the point； the nearer you must bring it to observe the light； and at whatever distance you see the light； you may draw off the electrical fire and destroy the repellency。 If a cork ball so suspended be repelled by the tube； and a point be presented quick to it； though at a considerable distance； 'tis surprising to see how suddenly it flies back to the tube。 Points of wood will do as well as those of iron； provided the wood is not dry； for perfectly dry wood will no more conduct electricity than sealing…wax。 〃To show that points will THROW OFF as well as DRAW OFF the electrical fire； lay a long； sharp needle upon the shot； and you cannot electrify the shot so as to make it repel the cork ball。 Or fix a needle to the end of a suspended gun…barrel or iron rod； so as to point beyond it like a little bayonet； and while it remains there； the gun…barrel or rod cannot； by applying the tube to the other end； be electrified so as to give a spark； the fire continually running ou
