1820.] Dr. Clarke on Crystallization of Sal lad Oil. 329 



exact place which he was entitled to occupy ; but often plvice 

 him much lower than the seat which his abihties and industry 

 would have entitled him to occupy, had he been satisfied with 

 that share of reputation which his real merit entitled him to 

 obtain. The conduct of Bradley was exactly the opposite ; yet 

 few men enjoyed a higher reputation, or were more respected by 

 all that was great and eminent in Great Britain or on the Conti- 

 nent during his own life time ; and few men have retained, or 

 are hkely to retain, a higher place in the most exalted and most 

 perfect of all the sciences. 



Article II. 



Regular Crystallization of Olive Oil. By Dr. Clarke, Profes- 

 sor of Muieralogy, Cambridge. 



(To Dr. Thomson.) 



DEAR SIR, Cambridge, March22, 1820. 



Ai\ accident has occurred within the last week which has 

 enabled me distinctly to observe the regular crystallization of 

 olive oil. The thermometer of Fahrenheit, during the late 

 north winds, has frequently indicated a temperature below 40° at 

 noon-day. Upon one of these occasions, when the mercury had 

 fallen, towards evening, to '35°, some sallad oil, instead of exhi- 

 bitmg the usual appearance, by congelation, of having lost its 

 transparency, presented to the eye a number of white, opaque, 

 prismatic radii, rising upwards from the bottom of the vessel, and 

 beautifully diverging in the transparent fluid. When examined 

 with a lens, these prisms (which were as large as the capillary 

 prisms of radiating arragonite in porous trap) were found to have 

 the form of mesotype ; that is to say, rectangular four-sided pnsms 

 with square bases. The terminating planes, being squares, 

 reflected the light in such a manner as to enable me to discern 

 their form in the most satisfactory manner. Several persons 

 witnessed this appearance; and among others our oeolop-ical 

 Professor, Sedgetvick, and Mr. Hendoir, of St. John's Colfege. 

 I endeavoured to preserve the oil in this state, but the weather 

 becoming warmer, the whole of the fluid became transparent. 

 Its crystalline appearance was, however, preserved durino- 

 24 hours; and often, during this time, examined. The 

 inference I would deduce from this circumstance is, that 

 the crystallization of this vegetable oil agrees with the general 

 phenomena of ci-ystallization characteristic of non-metallic com- 

 bustibles ; among which the octahedron, whether regular, as in 

 diamond; or obtuse, as in mellite ; or acute, as in sulphur; exhi- 

 bits pyramids whose bases are squares. 



E. D. Clakke. 

 8 



