342 COSMOS. 



IGOO, under the title of " Physiology of Magnets and of the 

 Earth as a great Magnet (d^ magno magnete tellure)." " The 

 property," says Gilbert, " of attracting light substances, Avhen 

 rubbe.], be their nature m hat it may, is not pecuUar to amber, 

 which is a condensed earthy jui.e cast up by the waves of 

 th^ se.i, and in which flying insects, ants, and worms lie en- 

 tombed as in eternal sepulchers (aeternis sepulchri^). The 

 force of attraction belongs to a whole class of very different 

 substances, as glass, sulphur, sealing wax, and all resinous sub- 

 stances, rock crystal, and all precious stones, alum, and rock 

 salt." Gilbert measuredthe strength of the excited electrici- 

 ty by means of a small needle, not made of iron, which moved 

 freely on a pivot {versorium electricuiii), and perfectly similar 

 to the apparatus used by Haiiy and Brewster in testing the 

 electricity excited in minerals by heat and friction. "Fric- 

 tion," says Gilbert further, " is productive of a stronger ef- 

 fect in dry than in humid air ; and rubbing with silk cloths 

 is most advantageous. The globe is held together as by an 

 electric force (?) Globus telluris per se electrice congregatur 

 et cohneret ; for the tendency of the electric action is to pro- 

 duce the cohesive accumulation of matter (motus electricus 

 est motus coacervationis materioe)." In these obscure ax- 

 ioms we trace the recognition oi terrestrial electricity — the ex- 

 pression of a force — which, like magnetism, appertains as 

 such to matter. As yet we meet with no allusions to re- 

 pulsion, or the difference between insulators and conductors. 

 Otto von Guerickc, the ingenious inventor of the air pump, 

 was the first who observed any thing more than mere phenom- 

 ena of attraction. In his experiments with a rubbed piece 

 of sulphur, he recognized the phenomena of repulsion, which 



nostris motionibus coi'pora allicere vldentnr, Electrica ct Magnetica; 

 Electrica naturalibus ab humore effluviis ; Magnetica fonnalibus effi- 

 cientiis seu potias primariis vigoribiis, incitationes faciunt. Facile est 

 hominibus ingenio acutis, absque experimentis et iisn rerum labi, et 

 errare. Substantiaj proprietates aut familiaritates, sunt generales ni- 

 mis, nee tamen verce designatce causre, atque, ut ita dicam, verba qnre- 

 dam sonant, re ipsa nihil in specie ostendunt. Neque ista succini <".re- 

 dita attractio, a singular! aliqua proprietate substantia, aut familiarita- 

 te assurgit; cum in pluribus aliis corporibus eundem effeetum, majori 

 industria invenimus, et omnia etiam coi'pora cujusmodicunque proprie- 

 tatis, ab omnibus illiis alliciuntur." {De ]\fa(jnete, p. 50, 51, 60, and 

 65.) Gilbert's principal labors appear to fall between the years from 

 1590 to 1600. Whewell justly assigns him an important place among 

 those whom he terms "practical reformers of the physical sciences." 

 Gilbert was surgeon to Queen Elizabeth and James I., and died in 

 1603. After his death there appeared a second work, entitled " Z>e 

 Mnndo nostra Suhhinari P'l/losnjt/tla Xova."' 



