449 



RECTIFICATIONS AND ADDITIONS. 



Page 32. 



A STILL much higher result for the earth's density than 

 was obtained by Baily (1842) and by Reich (1847-1850) 

 has been given by the pendulum experiments which 

 Airy instituted, with exemplary precautions, in 1854, 

 in the Harton coal-mine. The result of these experi- 

 ments is to give the density 6*566, with a probable 

 error of 0-182 (Airy, in the Phil. Trans. 1856, p. 342). 

 A small modification of this numerical value is added 

 by Professor Stokes, on account of the effect of the 

 earth's rotation and ellipticity, and alters the density to 

 6-565 for Harton, which is in 54 48' K lat., and to 

 6-489 for the equator. 



Page 80, line 5. 



Arago left behind him a rich mass of magnetic obser- 

 vations (more than 52,600 in number), obtained from 

 1818 to 1835, which, after a laborious redaction by 

 M. Fedor Thoman, have been published in the "GEuvres 

 completes de Francois Arago" (tome iv. p. 498). 

 General Sabine has discovered in -these observations (for 



VOL. IV. G G 



