Mr Barlow's Electro-Magnetic^ Experiments, 371 
Electro-Magnetic Experiments. 
The following very interesting experiments are selected from 
Mr Barlow’s section on this subject, the greater number of those 
which we have omitted having been previously given in this 
work. 
Exp. I. To exhibit the rotation of a galvanic wire round d 
magnet , and the reverse. 
Mr Faraday’s first apparatus for this purpose, has already 
been given in Vol. VI. p. 178, and 223. and 224. Note. He 
afterwards invented another apparatus, requiring a less galvanic 
action, which is shewn in Fig. 2. Plate VII. 
66 It consists of a piece of glass tube, the bottom part of which 
is closed by a cork, and through it is passed a small piece of 
soft iron-wire, so as to project above and below the cork. A 
little mercury is then poured in, to form a channel between the 
iron-wire and the glass-tube. The upper orifice is also closed 
by a cork, through which a piece of platinum- wire passes, being 
terminated within by a loop ; another piece of wire hangs from 
this by a loop, and its lower end, which dips a very little way 
into the mercury, being amalgamated, it is preserved from ad- 
hering either to the iron-wire or the glass. A very minute gal- 
vanic power being applied, by a contact with the lower and up- 
per end of the apparatus, arid the pole of a strong magnet being 
applied to the external end of the lower iron-wire, the moveable 
wire within begins rapidly to rotate round the temporary mag- 
net thus formed ; and this rotation may be inverted either by 
changing the contact, or by inverting the magnet. Mr Faraday 
states that this instrument is so sensible, that a rotation has been: 
produced in it by two plates, each only one inch square. 
Exp. II. 44 To exhibit the rotation of a magnet on its axis by 
the effect of a galvanic wire . 
i6 Let ABDE, Fig. 3., represent a cup of glass of wood, NS 
a magnet, having at its lower extremity a fine steel point, insert- 
ed in the agate a; be is a thin slip of brass or ivory, having a 
hole through which the magnet passes freely, and by means of 
which it is kept perpendicular : at the upper extremity N of the" 
a a 2 
