J. Nicklés on Different Applications of Magnetic Attraction. 345 
In this experiment the wheels did not rest on the rail as in or- 
dinary conditions: by means of the grease-box reversed of each, 
they were fixed upona framework for their support ; two wooden 
pulleys were arranged on the motor axle; these pulleys, in con- 
nection with the power wheel of the work shop, were calculated _ 
so as to furnish the two velocities of rotation, registered in the 
table. The rail placed below each wheel was moveable at one 
of its extremities, around a bolt, and carried at the other, a box of 
. zine for receiving the weight necessary for detaching the rail from 
the wheel when it was suspended by the magnetising action; a 
reservoir of water, divided into litres, was arranged so as to turn 
into each box the water necessary for breaking the connection. 
Kowing the length of the rail, its weight, the same of the box 
of zine, and the quantity of water required from the reservoir, we 
may, by a simple calculation, ascertain the amount sustained by 
the point of contact, and thence the pressure due to the magnetisa- 
tion, either during rest or rotation. 
In this way the table above has been obtained. 'The decrease 
observed during rotation was also exhibited in the following man- 
ner. The rail resting at its free extremity on a block of wood, 
and being separated from the wheel by an interval of 0-17 metre, 
a small magnetic declination needle placed at a distance of 0-75 
metre from the rail, was moved along the the wheel in order to 
ascertain the points where its direction was perpendicular to the 
ane of the wheel. 
When the wheel was at rest, the needle took a position vertical 
to the rails only when in a vertical plane passing by the axte, 
and consequently at the point of contact with the wheel. When 
on the contrary, the wheel was in motion, it was necessary to 
change the place of the needle, moving it backward (in relation to 
the direction of the movement of the wheel) in order to obtain the 
direction normal to the rails. ‘This change of place amounted to 
0°33 and 0-39 m. for velocities corresponding to rates of 18 and 
36 kilometers to the hour. 
These observations show that the resultant of the magnetic forces 
which passes by the centre of gravity of the helix, and consequently 
