1826.] an improved Electro-magnetic Apparatus. 361 



Fig. 8, a horse-shoe magnet, mounted with two mercurial 

 troughs r r, (fig. 9 shows one separate) t t two cylinders sus- 

 pended on the ends of the magnets, by points within their crowns 

 under the cupsiJv; their bottom edges are filed away, leaving 

 only four points (as fig. 10) to touch the mercury, by which 

 means the friction is much lessened. The troughs are adjusted 

 by the screws u u so as to bring the mercury just in contact with 

 the points of the cylinder; the screw points of the upper cups c c 

 just touch the mercury in the cups v. Upon making the com- 

 munications as before with the cups z z and c c, the cyUnders 

 will revolve as shown by the arrows. 



Figs 1 1 and 12 show a front and back view of a dipping needle, 

 mounted between two wires, o and p ; they are here placed in 

 the direction of the dip, but the quadrant i allows them to move 

 one quarter round, or to the equator of the magnet, as shown by 

 dotted lines. In their present position the needle will deviate^ 

 as figs 4 and 5 ; and it will be seen the needle cannot take a 

 position quite at right angles to the wire, owing to the 

 terrestrial magnetism drawing it on one side ; but when the 

 wires are carried round to the dotted position fig. 11, the 

 needle remaining as it was, so as to be at right angles ta 

 each other, then on passing the current from z through the 

 wire o, no effect will appear to take place, the needle is only 

 more confirmed to its position, but on passing it through p p, 

 the needle goes round, and dips with its south pole. The wire 

 passes through the wooden cup z, but the two ends of it p and 

 only just enter their respective wooden cups cc; these 

 wooden cups are placed at an angle of 45° to the horizon, so that 

 in either position they are similar, and will hold mercury enough 

 to make the contact. 



Fig. 13 shows two of the connecting wires separate, three or 

 four pairs of each of these are required. 



These figures are nearly one-fifth of the real size, and it will 

 be seen that the magnetic power is very great in proportion to 

 the galvanic power. 



Article VIII. 



Further Observations on the Genus Hinnites, with the addition of 

 another rece?it Species, indigenous to Great Britain, By J, E. 

 Gray, Esq. FGS. 



(To the Editors of the Annals of Philosophy/.) 



GENTLEMEN, Paris, Oct. 1 6, 1 826. 



In the number for August last, p. 103, I described a recent 

 species of the genus Hinnites of Mr. De France, which I had dis- 

 covered in the collection of the British Museum. A few days 



