Terrestrial Magnetism. 149 



and was repelled from the wick, the ends being invariably re- 

 versed in changing its course, I observe that having repeatedly 

 examined other candles, I have not been able to discover any 

 thing more than the ordinary capillary attraction in them ; and 

 am led to believe the repulsion in the case cited, was owing to an 

 accidental evolution of minute bubbles of gas at the base of the 

 exposed wick. I am strengthened in this opinion, by having ob- 

 served some time ago a similar phenomenon in an ash-hopper 

 while in operation, in which the cause was obvious ; the calm, 

 supernatant water, appeared to be very gently directed to several 

 little vertices, bearing thither fragments of coal, &c. ; as soon as 

 they reached the center, a small bubble of air arose in that spot ; 

 and bursting, caused the particles adjacent to wheel about and re- 

 treat. 



Tooth and Grinder of a Mastodon. — The grinder of a Mas- 

 todon ?* and the tusk of an Elephant have been found in this 

 State ; the first sixteen, and the second thirty miles from this 

 place. The tusk was disinterred from a bed of gravel : it must 

 have been originally at least six feet in length. Both specimens 

 are now in our " Atheneum." 



Art. XYIII. — On Terrestrial Magnetism; by John Locke, 

 M. D., Professor of Chemistry and Pharmacy in the Medical 

 College of Ohio. 



Medical College of Ohio, Nov. 20, 1840. 



TO THE EDITORS. 



You are already apprised that there was an erratum in my last 

 manuscript, published in Vol. xxxix, p. 319, of this Journal, mak- 

 ing an apparent disagreement in the results by the two dipping 

 needles at Davenport, in Iowa, amounting to 6^75. As the object 

 of that communication was to show that the separate results ob- 



* Dr. Plummer's mark of interrogation, implies a doubt which we presume will 

 be easily removed by an examination of the tooth; if of an elephant, it should 

 have low processes and the enamel bounding them should extend vertically through 

 from top to bottom ; if of the mastodon, the processes will be high and strong, and 

 the enamel only superficial over the entire tooth. — Sen. Ed. 



