1841.] Descriptioti of a Persian Astrolabe. 761 



recess, in which the trelliced circle represented by Plate II. revolves, 

 is divided into 360°, a mode of graduation vrell known to the ancients 

 I have also refrained from introducing drawings of all the Planispheres; 

 since the doing so would have swelled the number of plates to fourteen, 

 without, at the same time, disclosing a new truth, or illustrating an old 

 one. 



Premising these general observations, I shall now proceed to more 

 particular explanation, throughout which, agreeably to my plan, I 

 shall abstain from introduction o*f the abstract forms of science. I 

 shall also, for greater perspicuity, subdivide my description, and arrange 

 it under heads corresponding with the purposes which the instrument 

 is intended to serve; viz. those of Astronomy, Astrology, Geography — 

 and first of its 



Astronomy. — ^I have already said, that but little new can be adduced 

 on the subject of the Astrolabe, and the same remark applies to Arabian 

 science generally. The admirable works which the French savans 

 have conferred upon the world on the Astronomy of the Ancients, leave 

 but meagre gleanings for whoever may follow, especially in respect to 

 Arabian astronomy. I shall therefore in the following remarks confine 

 myself to a description of the astronomical uses for which the instru- 

 ment in question was probably intended, and refer such who would 

 acquaint themselves with the principles employed in its construction, 

 to the " Astronomie Ancienne" of Delembre.* 



In Plate I, which represents the back of the Astrolabe; the upper 

 limb is divided from the left and right ; or, as the Arabs express it, from 

 the east and west points, into two equal parts, terminating on the 

 highest, or zenith point ; these quadrantal arcs are again subdivided 

 into ninety equal parts or degrees, " the use of the limb thus graduated, 

 is for observation of the altitudes of celestial bodies, whether for 

 ascertainment of the latitude, or of the time. The instrument, it is 

 true, might be employed with even greater accuracy for the determi- 

 nation of terrestrial heights and distances, but I am not aware that 

 the Arabs ever do employ it for such purposes ; the manner in which 

 the Astrolabe is used, is this : the label, or index, Plate I. Fig. b. is 

 fixed upon its back by its axis c, which not only secures it there, but 



* qu: Bailly? Ed. 



