1 36 ULTRAMARINE. 



gravity, will carry him downward in the projectile curre, 

 and (whatever may be the height of the vehicle) he will 

 come to the ground with nearly the same force as if he 

 had leaped from it while he was standing still, only that 

 posite direc-^" ^^ ^^^^^ ^^^^ "* ^" opposite direction, and must take care 

 tion. to throw himself in such a position that he does not fall 



backwards when he touches the ground. 



From the result of this calculation a person run away 



with in an open carriage may judge how far this mode of 



escaping will be preferable as to safety. 



If a gig be For instance, if a gig is hung so low as to be an easy 



leap will pro- ^®*P ^^^^^ standing Still, he will probably receive little in- 



bablybceasy. jury by leaping out of it when it is going at the rate of 



15, or perhaps even 16, miles an hour, but not more. If 



he ventures to jump out at the side, the violence with 



which he would fall to the ground would be almost double, 



although the height might not be so great. 



J. E. CONANT. 



IX. 



Memoir on Ultramarine^ by Messrs. Desormes and Cle- 

 ment ; read to the Class of Physical and Mathematical 

 Sciences of the Institute^ January 27^ 1806*. 



Ultramarine -J*- HE fine blue colour known by the name of ulfra- 

 not yet exa- marine, has not yet 'been ai? object of research to che- 

 mists, who have hitherio turned their attention to the 

 lapis lazuli, which may in some sort be considered as its 

 One crystalliz- ore, and which has never exhibited itself in a crystalline 



ed sptcimen of form, except in a single specimen possessed by Mr. 

 lapi^ lazuli* -~ 



Guyton. 



Process of ex- To extract the ultramarine from its ore, a process is 

 markief " ^'^^' employed, to which art offers nothing analogous, and of 

 the theory of which we are totally ignorant. This pro- 

 cess consists in levigating the lapis lazuli, and mixing it 

 well with a melted composition of resin, wax, and linseed 

 oil. When these are thoroughly mixed, the compound 

 is suflfered to rool, and then well ground with a pestle, 



♦ Annales dc Chimle, Vol. LVlI. p. 317. 



or 



