382 M. J. Nicklés on a New System of Electro-magnets. 
2. Horse-shoe Magnets.—As the horse-shoe magnet is only 2 
curved bar with a helix about either extremity, the same results 
would be expected as with straight bar-magnets, that is, the in- 
crease in the length of the arms should exert an influence on the 
attraction produced by each of the poles when these poles act 
} will mention some of the results which I have obtained, 
bearing in this direction. 
The electro-magnet employed was the system of Mr. Joule,* 
except that the coarse wire was replaced by 60 metres of wire 1 
- millimeter in section, making a coil of 324 turns. 
f ° i t . 
fang Of Reduced current, — 
Total current, 5 
Tron added to the Weight borne by Iron added to the Weight borne by 
N. Pole. the S. Pole. S. Pole. the N. Pole. 
0 grammes. 180 gr. 0 gr. 175-190 gr. 
174 B2B is) 174 335 
15° 10’ 
Current tang. =: ca 
320 440 320 
‘The same results have been obtained with horse-shoe magnets 
of different forms, and also with the electro-magnet of 3 arms or 
trifurcate, which variety is the special subject of this notice. 
Hence the proposition of M. Dub is true, as long as the arma- 
ture is in contact with only one pole of the magnet. But we 
shall show that this is not so, when both poles act together. 
e experiments were made with two horse-shoe magnets of 
the same section (0-010) and of different lengths; one, 4 de- 
cimeters in total length, the other 8. The helices bad each 665 
turns of a copper wire, 1 millimeter in section; they were free, 
so that they might easily be removed. I will call the smaller 
magnet b, and the larger, 6’. The intensities of the current were 
ascertained by means of a rheostat. 
hese determinations had been already made when the me- 
moir of M. Despretz appeared, on the non-proportionality ene 
the tangents of the deviations and the intensities. But it ae = 
no use to apply to these experiments, or to the following, the for 
mula of M. Despretz, as they have special reference to the 0.4 
erties of electro-magnets, leaving out of view the currents whic 
act in t : 
The weights carried by the two opposite poles, were 28 
grammes as follows: 
Tan. 4° 20/ Tan. 7° 40) Tan. ee 
5100 ‘ 7500 gr. 10500 gr. 
5 : grammes . gr 10700 
5100. , 
* Annals of Electricity, v, 187. 
