1842.] Observations on the Herat Astrolabe. 721 



should therefore be carefully examined, and their law of position dis- 

 covered, to serve as a clue to their use. 



Perhaps I may be allowed to say, that from what I have seen 

 or read of the Astronomy of the Hindoos, and also of the Arabs, 

 my own mind has been brought to the conviction, that their knowledge 

 has been very much over-rated. Their knowledge appears to have 

 shewn itself chiefly in the calculation of eclipses ; and the phenomena of 

 eclipses being striking and capable of observation by persons of all des- 

 criptions, the powers of calculation which have led to their prediction, 

 have excited admiration, and raised the fame of the calculators. But the 

 calculation of eclipses is not so very profound a branch of Astronomy, 

 at least when carried only to the degree of accuracy shewn in Hindoo 

 calculations, as to entitle the Hindoo astronomers to any great fame, 

 except as being attentive observers and moderate geometers. But as to 

 any physical laws, they seem to have been profoundly ignorant, and 

 therefore could not have been mathematical or " physical" astronomers. 

 Ancient observations are of great value in Physical Astronomy; for 

 instance, the mere fact of an eclipse having been seen by the Chaldeans 

 on a certain day, and at a certain hour in the year b. c. 720, has 

 led modern astronomers to the demonstrable conclusion, that the 

 length of the mean day has not changed by a hundred and fifteenth 

 part of a second of time within the last twenty-five centuries. This 

 physical fact, of great importance in all theories regarding terrestrial 

 heat, and therefore in the researches of Physical Geology, could not 

 have been demonstrated without the observed fact of the Chaldean 

 astronomers. But this observation, (though important in its historical 

 consequences,) does not argue any great power and knowledge in 

 the observers. AW facts of observation are in a similar way valuable, 

 but do not necessarily prove that the observers are profound philo- 

 sophers. In this way, by confounding the value of observations with 

 the powers necessary for conducting and recording them, it occurs 

 to me, that the Hindoo and Arabian astronomers have received, in 

 general estimation, far too high a name. 



Bishop's Palace, Calcutta, August Wth, 1842. 



