Formation of Rocking Stones. 359 



Mi • ■ • dgj d Pi • • • d pJ = Mi ■ • ■ Mr! Mi • • • ^» 



4/ 







(4) 



On the left side the motion is defined by the initial #'s and p's 

 at time t'; on the right by the initial and final g's and by 

 t—t 1 (not E, which is a dependent variable). 

 In like manner 



Ml • • ■ <fy w d Pl • ' • d Pn = Ml ' ' ' <*?»' ^1 ' ' * rf & 



fej dp n 



dqi ■ * • 



' ' - dqi' 





dp, 



dp n 



(5) 



By the relation (3) proved above the two determinants in (4) 

 and (5) are equal, and thus 



Ml • • • Mr! d P\ ' • ' d Pn=Ml -"Mndpi... dp n , . (5) 



the required conclusion. 

 February 20. 



XXXIX. On an Experiment Illustrative of the Formation of 

 Rocking Stones. By Chaeles Tomlinson, F.R.S.* 



IN an article on the u Weathering of Kocks " (Phil. Mag. 

 Dec. 1888), I noticed the explanation given by Dr. 

 Paris and Mr. Justice Grove on the formation of logging 

 or rocking stones, and stated that the process described by 

 them might be imitated by small blocks of camphor freely 

 exposed to evaporation in the air. 



Camphor is now sold in neatly cut parallelopipeds, oblong 

 and square. A square block, 1^ inch to the side, and half 

 an inch thick was superposed upon one of similar dimensions 

 (fig. 1), and placed in the glass pan of a pair of scales close to 



* Communicated by the Author. 



