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396 Foreign Literature and Science. 



If this ring have a diameter of three or four inches, and 

 the instrument be not too heavy, it possesses the power of 

 seJf direction, always arranging itself in a plane perpendic- 

 ular to the magnetic meridian. Bib, XJniv* 



efteci of 



tsfi 



journals. One* of these, by P. Barlow, Esq. of the Royal 

 Military Academy, is as follows : — 



*^ A B (see the plate at the end) is a rectangular piece of 

 hard wood; C D E a stout piece of brass or copper wire 

 and abed, a rectangle of smaller copper coin, (sol- 

 dered at E) on the lower side of which the wheel W of thin 

 copper turns freely:/"^ is a small reservoir of mercury 

 sunk in the wood; t g i a narrow channel running into it. 

 H M is a strong horse shoe magnet. 



"Mercury being now poured into the reservoir/^ till 

 the teeth of the wheel are slightly immersed in it, and the 

 surface covered with weak diluted nitric acid, make the 

 connection with the battery at i and D: and the w^heel W 

 will immediately begin to rotate with an astonishing velocity, 

 far beyond the power of the eye to follow, and will thus 

 produce the most pleasing effect." 



*'The galvanic apparatus which I employed to produce 

 this motion was the Calorimotor of Dr. Hare which I had 

 made of the plates of my old battery, 20 of zinc and 20 

 of copper, each ten inches square. But a much less pow- 

 erful combination will be sufficient." 



The suspension of the wheel is shewn in figure 2, and 

 it may be proper to add, that in order to ensure a complete 

 contact, the two sockets, or the end of the spindle, should 

 be amalgamated, as also the tops of the points of the wheel. 



^' If the contact be changed, or if the magnet be reversed, 

 the motion of the wheel will be reversed also: but I find 

 the best effect produced when the wheel turns inward. 



42. An Iron Steam Boat has recently made a voyage 

 from London to Kouen in 55 hours, and then proceeded to 

 Paris. This is doubtless the first attempt to traverse the 

 ocean in a vessel composed of any material but wood. 



*• For the other, see Phil. Mag. for June, pa. 434. 



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