Magnetic Influence of Solar Light. 257 



they are again drawn along it, and so on, until it has become 

 sufficiently magnetised. The needle above referred to, was 

 found after magnetization, to have acquired a northern 

 polarity at its point, and a southern polarity at its eye 

 extremities, by which I mean, that the former pointed to the 

 north pole, the latter to the south pole of the earth. The 

 polarities really acquired were therefore the converse of 

 those I have stated, but custom has sanctioned the change of 

 terms, and that point of a needle which turns to the north, 

 is invariably called the north pole, although southern pola- 

 rity really exists in it. Some writers insist on using the 

 rigidly correct terms, and calling the common north pole of 

 the magnet the south pole, but this has led to much confu- 

 sion, and if any change at all is adopted, the best undoubted- 

 ly would be to dispense entirely with the terms north and 

 south, and to call the end of the needle that turns to the 

 north pole of the earth, the marked, and the other the 

 unmarked end, as is frequently done by the best authorities. 

 To return, however, the magnetised needle was suspended 

 by means of a single filament of silk within a glass cylinder 

 open at both ends, about six inches in height, and two 

 inches in diameter, so that the needle vibrated freely within 

 it. This apparatus was then arranged over a slit in a table, 

 through which slit the wires or cylinders to be tested were 

 placed in front of the testing needle, and could be raised or 

 depressed in any way that was necessary. When the needle 

 became stationary in the magnetic meridian, a mark was 

 made on the glass cylinder exactly opposite the north pole, 

 and another mark about 45° to the east of this ; from the 

 latter mark the registered oscillations commenced; and it 

 remained constant throughout each series of observations. 

 The method of observation employed was first to register 

 the duration of a certain number of vibrations of the testing 

 needle, with the wire under experiment placed at a certain 

 known distance in front of it, before exposure to the sun's 



