550 COSMOS. 



The enjoyment of a long peace might certainly have led us 

 to expect, that the union under one empire of extensive coun- 

 tries having the most varied climates, and the facility with 

 which the officers of state, often accompanied by a numerous 

 train of learned men, were able to traverse the provinces, 

 would have been attended, to a remarkable extent, by an 

 advance not only in geography but in all branches of natural 

 science, and by the acquisition of a more correct knowledge of 

 the connection existing among the phenomena of nature : yet 

 such high expectations were not fulfilled. In this long period 

 of undivided Roman empire, embracing a term of almost four 

 centuries, the names of Dioscorides the Cilician, and Galen of 

 Pergamus, have alone been transmitted to us as those of 

 observers of nature. The first of these, who increased so con- 

 siderably the number of the described species of plants, is far 

 inferior to the philosophically combining Theophrastes, whilst 

 the delicacy of his manner of dissecting, and the extent of his 

 physiological discoveries, place Galen, who extended his 

 observations to various genera of animals, " very nearly as 

 high as Aristotle, and, in some respects, even above him." 

 This judgment embodies the views of Cuvier.* 



Besides Dioscorides and Galen, our attention is called to a 

 third and great name that of Ptolemy. I do not mention 

 him here as an astronomical systematise!*, or as a geographer, 

 but as an experimental physicist, who measured refraction, 

 and who may, therefore, be regarded as the founder of an im- 

 portant branch of optical science, although his incontestible 

 claim to this title has been but recently admitted. f However 



* Cuvier, Hist, des Sciences naturelles, t. i. pp. 312--328. 



i 1 Liber Ptholemei de opticis sive aspedibus; a rare manuscript 

 of the Eoyal Library at Paris (No. 7310), which I examined on the occa- 

 sion of discovering a remarkable passage on the refraction of rays in 

 Sextus Empiricus (adversus Astrologos, lib. v. p. 351, Fabr.). The 

 extracts which I made from the Paris manuscript in 1811 (therefore 

 before Delambre and Venturi), will be found in the introduction to my 

 Eecueil d 'Observations astro nomiques, t. i. pp. Ixv.-lxx. The Greek 

 original has not been preserved to us, and we have only a Latin translation 

 of two Arabic manuscripts of Ptolemy's Optics. The name of the Latin 

 translator was Amiracus Eugenius, Siculus. Compare Venturi, Com- 

 ment, sopra la storia e le teorie deW Ottica, Bologna, 1814, p. 227; 

 Delambre, Hist, de I Astronomic ancienne, 1817, t. i.p. 61, and t. ii. pp. 

 410-432. 



