lly 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。
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 ignoredsuch 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 considerabl