460 EDITOR'S NOTES. 



lengths referred to in the preceding paragraph, yet, as 

 the conclusions which have been here reproduced are 

 taken from my publication in 1825 (which publication 

 was anterior to 1828, the epoch of the announcement of 

 Bessel's discovery), it may be proper on this occasion 

 to state explicitly the degree in which those conclu- 

 sions were affected by it. It is conformable to the 

 plan of this volume of e ( Kosmos " (which treats of the 

 " special results of observation in the domain of the ter- 

 restrial phenomena "), that it should contain the data 

 upon which important conclusions are based, corrected 

 according to the most recent emendations. Now Bessel 

 has shown that when a pendulum moves in air the air 

 becomes part of the moving system, and the moving 

 force must be imparted, not only to the particles of 

 mass of the solid body of the pendulum, but also to 

 all the particles of mass of the air which are put in 

 motion in accompaniment with it. The specific gravity 

 of the moving mass, including solid and gaseous, being 

 less than that of the solid part alone, the method em- 

 ployed antecedently for computing the effect of the me- 

 dium in which the pendulum was vibrated, in retarding 

 the vibration, was erroneous ; and, as the quantity and 

 distribution of the air accompanying the solid- portion of 

 the pendulum must depend upon the form and ar- 

 rangement of the solid part, it followed that the true 

 "correction for buoyancy" for each particular form of 

 experimental pendulum required to be ascertained by 

 special experiment. It was obvious that in the case of 

 the determinations of absolute length, as the apparatus 

 of Borda and that of Rater's convertible pendulum 

 differed widely in form, their respective corrections for 



