DISCOVERIES IN THE CELESTIAL SPACES. 341 



precipitated water was determined by weight.* In addition 

 to the condensation-hygrometer, which, by the aid of the ideas 

 of Le Roy in our own times, has gradually led to the exact 

 psychrometrical methods of Dalton, Daniell, and August, we 

 have (in accordance with the examples set by Leonardo da 

 Vi licit) the absorption-hygrometer, composed of substances 

 taken from the animal and vegetable kingdoms, made by San- 

 tori (1625), Torricelli (1646), and Molineux. Catgut and the 

 spikes of grasses were employed almost simultaneously. In- 

 struments of this kind, which were based on the absorption by 

 organic substances of the aqueous vapor contained in the at- 

 mosphere, were furnished with indicators or pointers, and small 

 counter-weights, very similar in their construction to the hair 

 and whalebone hygrometers of Saussure and De Luc. The 

 instruments of the seventeenth century were, however, defi- 

 cient in the fixed points of dryness and humidity so necessary 

 to the comparison and comprehension of the results, and which 

 were at length determined by Regnault (setting aside the sus- 

 ceptibility acquired by time in the hygrometrical substances 

 employed). Pictet found the hair of a Guanche mummy 

 from Tenerifle, which was perhaps a thousand years old, suf- 

 ficiently susceptible in a Saussure's hygrometer. $ 



The electric process was recognized by William Gilbert as 

 the action of a proper natural force allied to the magnetic 

 force. The book in which this view is first expressed, and in 

 which the words electric force, electric emanations, and elec- 

 tric attraction are first used, is the work of which I have al- 

 ready frequently spoken, and which appeared in the year 



* Antinori, p. 45, and even in the Saggi, p. 17-19. 



t Veuturi, Essai stir les Ouvrages Physico-mathimatiques de Leonard 

 de Vinci, 1797, p. 28. 



% Bibliotheqne Universelle de Geneve, t. xxvii., 1824, p. 120. 



Gilbert, De Magnete, lib. ii.,cap. 2-4. p. 46-71. With respect to 

 the interpretation of the nomenclature employed, he already said, 

 Electrica qua attrahit eadem ratione ut electrum ; versorium non mag- 

 neticum ex quovis metallo, inserviens electricis experimentis. In the 

 text itself we find as follows : Maguetice ut ita dicam, vel electrice 

 attrahere (vim illam electricam nobis placet appellare . . . .) (p. 52) ; 

 effluvia electrica, attractiones electrica?. We do not find either the ab- 

 stract expression eleclricitas or the barbarous word magnetism-its intro- 

 duced in the eighteenth century. On the derivation of f/2.eK.Tpoi>, '' the 

 attractor and the attracting stone," from ITi^lq and IXkeiv, already in 

 dicated in the Timseua of Plato, p. 80, c, and the probable transition 

 through a harder iXenrpov, see Buttmann, Mythologus, 1x1. ii. (1829), 

 s. 357. Among the theoretical propositions put forward by Gilbert 

 (which are not always expressed with equal clearness), I give the fol- 

 lowing: "Cum duo sint corporum genera, qua? manifestis sensibus 



