“ 
’ Relation of pressure to sliding on dry rail, 
“ “ “ wet as 
254 M. J. Nickles on Friction and Pressure. 
a scale for receiving the necessary weights, to determine the foree 
of the magnetic attraction. This force, once known, the cord 
attached to the axis of the magnet was deétached, and another 
was applied a little above the poles, at the height of a small pul- 
ley; y, fastened to the extremity of the rail: this cord which 
passed between the arms of the magnet terminated in a small rod 
of copper which was secured to f, on the arms, where it was held 
by rivets. A second scale, P’, smaller than the preceding, re- 
ceived the weights required for moving the apparatus onward, In 
the plane of the rail. The experiment was tried with a dry at- 
mature, and also with one wet with well water. To the weight 
carried, given in the table, 4 kilograms should be added, for the 
electro-magnet, and this is noted in the column of means. _ More- 
over the horizontal sliding observed was a kilogram too great, 
this representing the effort to be overcome in causing the electro- 
magnet to slide when not magnetized, and this is deducted in 
the column of means. The results with the dry and wet rail are 
as ‘follows: 
ci aatdauaite With mane reeligtans AS SE erates Oe 7 oe oe 
Weight carried normally, i: Horizontal ‘Means Relations. 
or magnetic pressure. ie sliding. i 3s Le a 
Dry rail, 231 k, 73 30 
236 23214=236k.; 73 19~12=%3E 0 
229 "3 a ae 
Wet rail, 230 k. 63 k, yt 
224 237+4==231k.| 67 645-1635, 02 
63 
Pb 
The circuit being broken, a weight of 232 kil. was added 2 
the magnet, by means of the bar mm, supported on the pen 
the magnet; the cord directly below carried a pulley to wine? 
a scale for the weights was adapted. The pressure was at 
erted normally on the magnet. The magnet itself weigh ‘s 
kilograms; the charge was therefore 236 kil., which i abe 
the pressure exerted on the armature in the preceding experimen” 
Normal pressure. 
Means.| Horizontal sliding.) Means Relations. | 
fis coke Ry 
Dry rail, 236 k. 
236 k. 236 k, 68 fee 
63 a 
Wet rail, 236 k. 236 k. l236 k. Pd | Be re 
Wet rail, 250 | Sewee 
The results are hence as follows: so 
Magnetic pressure. Pressure by wel 
0-25 
It would have been interesting to have determined the oo 
of effort required to make the apparatus slide when both species 
ized and weighted, to ascertain if the result would be the — ' 
the two slidings. But an accident which happened preven 
the month 
the repetition of the experiments which were made in 
of January, 1851. 
