342 cosmos. 



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

 Earth as a great Magnet (de magno magnete 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 (acternis sepulchris). 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 measured the strength of the excited electrici- 

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

 freely on a pivot {vers&rium electricum), and perfectly similar 

 to the apparatus used by Hauy 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 (1) Globus telluris per se electrice congregatur et 

 cohaeret ; 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 motionibus corpora allicere videntur, Electrica et Magnetica; 

 Electrica naturalibus ab humore effluviis; Magnetica formalibus effi- 

 cientiis seu potias primariis vigoribus, incitationes faciunt. Facile est 

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

 errare. Substantive proprietates aut familiaritates, sunt generates nimis, 

 nee tameu verae designate causa?, atque, ut ita dicam, verba quaedam 

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

 attractio, a singulari aliqua proprietate substantia, aut familiaritate as- 

 surgit ; cum in pUnibus aliis corporibus eundem effectum, majori indus- 

 tria invenimus, et omnia etiam corpora cujusmodicunque proprietatis, 

 ab omnibus illiis alliciuntur." {De Magnete, 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 1., and died in 1603. After 

 his death there appeared a second work, entitled " De Mundo nostra 

 . Sublunari Philosopkia Nova. 7 ' 



