IIRI.IOCENTRIC PLACES OF JUPITER. 339 



It will be seen tbat in 1908- 1910 errors of either set of tables 

 were very small, and that Le WM'rier's were the better in 

 declination. 



Here I would like to call attention to the cause of the slip 

 I made, which does not in any way invalidate the argument of 

 the rest of the paper. It arises from the injudicious practice 

 of referring celestial co-ordinates to the two moving planes 

 of the ecliptic and equator. A little reflection will show that 

 in the case of heliocentric ct)-ordinates ''' the consideration of the 

 shifting planes of so insignificant a planet as the Earth is 

 gratuitous — the departure point and plane adopted in the Con- 

 iiaissaiirc dcs Tciiif^s are in constant motion, and by quantities 

 which are appreciable in a few hours. All considerati-..^ of the 

 effects of the shifting of the ecliptic and Earth's equator should 

 be left over until the preparation of the ephemeris in Right 

 Ascension and Declination. 



Academy of Natural Sciences, Philadelphia. 



— The centenary of the foundation of the Academy of Xatur;d 

 Sciences of Philadelph'ia was celebrated on the 19th, 20th. 

 and 2 1st March, 19 12. The functions were attended by 144 

 representatives of other learned societies that had been invited 

 to send delegates. The South African Association for the 

 Advancement of Science was represented by one of its past 

 presidents. Dr. Gardner F. Williams, M.A., LL.D.. at present 

 residing at Washington. At the opening meeting of the celebra- 

 tions, v.'hich took place in the Academy's Lecture Hall at 

 Philadelphia, the minutes of the Academy's first meeting, held 

 on the 2ist March. 1812. were read, and congratulatory letters 

 and cables were presented from 184 scientific societies and 

 instituticms in various parts of the world, including the Depart- 

 ment of Agriculture of the South African Union. An invita- 

 tion reception held by the President of the x^cademv, the Hon. 

 S. G. Dixon, M.D.. LL.D., at the Bellevue-Stratford Hotel on 

 March 20th, was attended by over one thousand guests. Th.e 

 proceedings concluded on the following evening with a banquet 

 in the Lecture Hall of the Academy. 



* Heliocentric co-ordinates : the place of a planet as seen by an imaginary 

 observer at the centre of the Sun. 



