on the Rates of Chronometers. 47 



part may be attributed to the uncertain intensity of tlie agent pro- 

 ducing- the aberrations, and part to the imperfect isochronism of 

 the time-keepers employed*; — the former producing necessarily 

 on the same chronometer variable effects, according to the differ- 

 ent degrees in which its energy is displayed, and to the different 

 positions 'assumed by the balance ; — and the latter, occasioning 

 in different chronometers, by the operation of the same cause, 

 alterations of rate, from less to greater, and from greater to 

 less. 



Plymouth, May 25th, 1824. 



Art. III. An Account of the Native Oil of Laurel. By 

 Dr. Hancock, of Demerary. 



g Essequebo, January 18, 1824. 



Aware of the interest you take in the progress of useful 

 discovery, and of your readiness to devote your columns to its 

 advancement, I take the liberty of communicating, for insertion in 

 your respectable Journal, a few observations on a very extraordi- 

 nary vegetable production, the knowledge of which has hitherto 

 been almost exclusively confined to the natives of Spanish Guiana. 

 This substance which has been very injudiciously termed Azeyte 

 de Sassafras, an appellation which tends to confound it with the 

 essential oil, yielded by the Laurus Sassafras, of the Northern 

 Continent of America, affords, so far as my knowledge extends, an 

 extraordinary and solitary instance of the production of a perfectly 

 volatile liquid, without the aid of art. Substituting for the appel- 

 lation to which I have objected, the provisional name " Native 

 Oil of Laurel," I shall describe the method of procuring it, and 

 enumerate its principal chemical and medicinal properties, so far 

 as they have been investigated and examined. 



The Native Oil is yielded by a tree of considerable magnitude ; 



• See an Essay in the 34th Number of this Journal, " On the AUcration^ 

 of Rate produced in different Chronometers, by the Influence of Magnetism y 



