468 Proceedings of the Royal Irish AcademTj. 



LXYIII. — The IxsTEUirEis'is i^^ the Old Obsektatoey at Peking. 

 By J. L. E. Deetee, II. A. 



[Read, June 13, 1881.] 



"Wheis^ the missionaries of the Society of Jesus, in the seventeenth 

 century, made their way to Peking, and startled the scientists of the 

 Celestial Empire by their superior knowledge, they found in the 

 eastern part of the city, on the rampart or wall surrounding it, an 

 astronomical ohservatory furnished with seyeral old instruments. 

 Eather Yerbiest gained the confidence of the Emperor by repeatedly 

 calculating beforehand the exact length of the shadow which a 

 gnomon would throw at noon, and was authorised to have constructed 

 six new large instruments. He has himself described these in a 

 work with the following title: — "Astronomia Europtea sub impera- 

 tore Tartaro Sinico Cam Hy appellato, ex umbra in lucem revocata a 

 E-. P. Eerdinando Yerbiest, Elandro Belga, e Societate Jesu, Acade- 

 miae astronomicse in regia Pe Kinensi Praefecto " (Dillingae, 1687, 

 4to).^ The old instruments, which had to be removed to make room 

 for his own, he seems to have paid no attention whatever to ; at least 

 he says nothing about them in his book, except (p. 47) that the 

 Emperor gave him leave to construct new instruments — " Prioribus 

 instrumentis Sinicis rudioris Minervse, quEe jam a trecentis proxime 

 annis speculam occupabant, inde amotis." . 



These despised instruments, as well as those erected by Father 

 Yerbiest, are still in existence. Some time ago I received from a 

 friend residing in China, llr. S. M. Eussell, a series of photographs of 

 these interesting scientific relics, and having had my attention drawn 

 to them in this way, I thought that a short account of them might be 

 read with some interest, particularly as there has not been much 

 published about them hitherto. 



The only plate in Yerbiest's book represents the platform on 

 which the six new instruments were mounted. It forms a square, 

 with two small additions to the north-east corner, one of which is the 

 head of the staircase leading up to the platform, while the other was 

 occupied by a small house to which the observers could retire in bad 

 weather. ISText the staircase, on the north side of the platform, was a 

 high mast, with a weathercock on it. I^ext to this was a sextant of six 

 feet radius {pedes geometrici), evidently an imitation of Tycho Brahe's 

 " Sextans bipartitus minoribus siderum distantiis inserviens," - which 

 it exactly resembles, with the exception that the arc is single. The arc 



^ This book seems to be rather scarce. Through the kindness of Father 

 Perry, F.R.S., I have been able to examine a copy of it. Delambre gives an 

 account of it in his Ristoire de rAstrononde dii Moycn Age, p. 213, et seq. 



"^ Astronomia instauratce Mechanica, fol. D 3. 



