342 COSMOS. 



1600, under the title of " Physiology of Magnets and of the 

 Earth as a great Magnet (de magno magneto tellure)." " The 

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

 rubbed, be their nature what it may, is not peculiar to amber, 

 which is a condensed earthy juice cast up by the waves of 

 the sea, and in which flying insects, ants, and worms lie en- 

 tombed as in eternal sepulchers (seternis sepulchris). The 

 force of attraction belongs to a whole class of very different 

 substances, as glass, sulphur, sf^aling wax, and all resinous sub- 

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

 salt." Gilbert measured the strength of the excited electrici- 

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

 freely on a pivot {versorium electricum), 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 effect 

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

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

 tric force C?) Globus telluris per se electrice congregatur et 

 cohseret ; for the tendency of the electric action is to produce 

 the cohesive accumulation of matter (motus electricus est mo- 

 tus coacervationis materise)." In these obscure axioms we 

 trace the recognition of terrestrial electricity — the expression 

 of a force — which, like magnetism, appertains as such to mat- 

 ter. As yet we meet with no allusions to repulsion, or the 

 difference between insulators and conductors. 



Otto von Guericke, 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 motiouibus corpora allicere videntur, Electrica et Magnetica; 

 Electrica naturalibus ab humore efHuviis; Magnetica fonnalibus effi 

 cientiis seu potius primariis vigoribus, incitatioues faciunt. Facile est 

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

 errare. Substantiae proprietates aut familiaritates, sunt generales nimis, 

 nee tamen verse designatae causae, atque, ut ita dicam, verba quaedam 

 sonant, re ipsd nihil in specie ostendunt. Neque ista succini credita 

 attractio, a singulari aliqu^ proprietate substantiae, aut familiaritate as- 

 surgit ; cum in pluribus aliis corporibus eundem efFectum, majori indus- 

 tria invenimus, et omnia etiam corpora cujusmodicunque propiietatis, 

 ab omnibus illiis alliciuiitur." (De Magnete, p. 50, 51, 60, and 65.) 

 Gilbert's principal labors appear to fall between the years from 1590 

 to IGOO. Whewell justly assigns him an important place among those 

 w^hom 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 " De Mundo nostre 

 Sublunari Philosophia Nova.'^ 



