THE AEABS. 591 



before Berthold Scliwarz, a species of gunpowder was used to 

 blast the rock in the Ilammelsberg, in the Harz mountains. 

 The invention of an air thermometer is also ascribed to 

 Avicenna from a notice by Sanctorius, but this notice is very 

 obscure, and six centuries passed before Galileo, Cornelius 

 Drebbel, and the Academia del Cimento, by the establishment 

 of an exact measurer of heat, created an important means for 

 penetrating into a world of unknown phenomena, and com- 

 prehending the cosmical connection of effects in the atmosphere, 

 the superimposed strata of the ocean, and the interior of the 

 earth; thus revealing phenomena whose regularity and 

 periodicity excite our astonishment. Among the advances 

 which science owes to the Arabs, it will be sufficient to 

 mention Alhazen's work on refraction, partly borrowed, 

 perhaps, from Ptolemy's Optics, and the knowledge and first 

 application of the pendulum as a means of measuring time, 

 due to the great astronomer, Ebn-Junis.* 



* Laplace, Precis del" Hist, de V Astronomic, 1821, p. 60; and Am. Sedil- 

 Memoire sur les Instrumens astr. des Ardbes, 1841, p. 44. Thomas 

 Young (Lectures on Natural Philosophy and the Mechanical Arts, 

 1807, vol. i. p. 191) does not either doubt that Ebn-Junis, at the end of 

 the tenth century, applied the pendulum to the measurement of time, but 

 lie ascribes the first combination of the pendulum with wheel-work to 

 Sanctorius, in 1612, therefore forty-four years before Huygens. With 

 reference to the very elaborately constructed clock included in the 

 presents which Haroun Al-Iiaschid, or rather the Caliph Abdallah, sent, 

 two hundred years earlier, from Persia to Charlemagne at Aix-la- 

 Chapelle, Eginhard distinctly says, that it was moved by water, (Horolo- 

 gium ex aurichalco arte mechanica mirifice compositum, in quo duode- 

 cim horarum cursus ad clepsidram vertebatur); Einhardi Annales, 

 in Pertz's Monumenta Germanice Historica, scriptorum, t. i. 1826, p. 

 195. Compare H. Mutius, De Germanorum origine, gestis, &c. 

 Chronic, lib. viii. p. 57, in Pistorii G&rmanicorum scriptorum, t. ii. 

 Francof. 1584; Bouquet, Recueil des Historians des Gaules, t. v. pp. 

 333 and 354. The hours were indicated by the sound of the fall of small 

 balls, and by the coming forth of small horsemen from as many opening 

 doors. The manner in which the water acted in such clocks may indeed 

 have been very different among the Chaldeans, who " weighed time " 

 (determining it by the weight of fluids), and in the clepsydras of the 

 Greeks and the Indians; for the hydraulic clockwork of Ctesibius, under 

 Ptolemy Euergetes II., which marked the (civil) hours throughout the 

 year at Alexandria, was never known, according to Ideler, under the 

 common denomination of K\e;}/vdpa. (Idelev's Handbuch derChronoiogie, 

 1825, bd. i. s. 231.) According to the description of Vitruvius Oib. ix. 



