Chemical Science. 



373 



the lamp. The second magnet is placed near F G, having its N end 

 upwards. If the lamp be beneath B, the rotation is in the direction 

 BGA; but if it be opposite to F G, the rotation is A G B. The 

 apparatus without the agate cap weighs 4 grains. 



2. Thermo-electric Rotation. — Mr. Marsh, of Woolwich, has also 

 constructed a variety of apparatus for the exhibition of rotation by 

 thermo-electricity. By the directions of Mr. Barlow, he endeavoured 

 to make an apparatus according to the former instructions of Professor 

 dimming, but, failing almost entirely in making it act, he constructed 

 some according to his own suggestion, which succeeded perfectly. 

 Fig. 1, will give an idea of this appa- 

 ratus; the double line represents silver 

 wire, the single line platina wire. They 

 are soldered together and made into a 

 rectangle, having a ring in the lower 

 part for the introduction of the support. 

 A fine point is attached to the upper part 

 of the rectangle, and resting on an agate 

 cap on the top of the support, allows of 

 free motion. When the pole of a mag- 

 net was placed as in the figure, and a 

 lamp applied at D, the instrument im- 

 mediately moved round until the side 

 E came to the flame, and then it moved 

 back again, at last resting at right an- 

 gles to the lamp and magnet. When a 

 second magnet was placed in a similar 

 position at D, and then the lamp ap- 

 plied either at D or E, rotation began, 

 which was either in one direction or 

 the other, according as the lamp was 

 applied to one end or the other, and soon amounted to thirty revo- 

 lutions in a minute. 



Compound rectangles were then made, having four branches, and 

 performed extremely well : the length of the rectangle is about two 

 inches, the deptk an inch, the diameter of the platinum wire. ^ of 

 an inch, and that of the silver -J^. When two rectangles were ar- 

 ranged on the poles of a horse-shoe magnet, as in Fig. 2, and the lamp 

 applied between them, they continue to revolve as long as the lamp 

 remains burning. , 



Mr. Barlow has made many experiments with these apparatus, 

 and finds them to accord perfectly with the laws he has laid down in 

 his Essay on Magnetic Attractions. Some singular appearances of 

 motion arc produced with the compound rectangle, when the mag- 

 in tic pole being considered as stationary, the lamp is applied beneath 

 U|e four branches in succession, but they are all reducible to 



