J. Nickiés on Different Application ef Magnetic Attraction. 341 
there is nothing to prevent making the magnetic checks to 
act upon the wheels. In either case, a power as energetic as de- 
sired may be developed, whose intensity may be varied at will, 
from that required to produce an instantaneous arrest of the 
mi as in cases of imminent danger, to that for ordinary stop- 
Pane different effects were produced with the small car rep- 
resented in figure 4. The element of a galvanic battery here 
employed, gives a force sufficient to stop the car instantly, even 
when driven at full speed it arrives at the bottom of a grade of 
190 millimeters. By diminishing the current or augmenting the 
charge, we produce on the contrary an effect which retards the 
motion of the vehicle and ends by stopping it altogether. By in- 
terrupting the current and reéstablishing it in turns the car may be 
made to leap along the track. These different effects, which are 
not well attempted with a large train, are readily shown ona 
small scale, and are calculated to interest much the young student. 
But it will be understood that my researches aim not merely to 
exhibit a new property of electro-magnets, and combine them in 
instructive apparatus. My plansare of anotherkind. They seek 
to contribute to railroads, a new and important improvement, 
and [ shall not be satisfied until it has become easy to use grades 
of more than 10 millimeters to the meter, and until it shall become 
no longer necessary to construct tunnels at great expense or to 
build extensive earth-works, or make curves of large radius. Of 
what avail otherwise the efforts to givea smaller size to the 
driving wheels, less weight to locomotives, lighter rails to the 
road, thereby to make a large diminution of expense in the con- 
struction and use of roads? Ifa smaller and lighter driving wheel 
a invented, the adhesion must be imparted to it which it fails 
having on account of its lightness, and hence it must be use- 
fas under the old system which works upon the paradox of mak 
ing a machine run better by giving it more weight. 
I have therefore sought to pass from the laboratory experiment 
to the actual locomotive in its own field. I have made my trials 
on the road between Paris and Lyons. The locomotive put at 
my dispo: sal was, in truth, somewhat worn by long. service, and 
one of its driving wheels ‘carried a ton of weight more than the 
other. I was not allowed to make any changes in the machine, 
and I was required to attach my apparatus in such a way that it 
might be easily removed. Notwithstanding the unfavorableness 
of these conditions I went to work, certain of having an effect suf- 
ficient to prove the spereateD possible. ‘This was admitted by 
: eee appointed by the minister of Public Works, consist- 
of MM. Pouillet, Regnault, Froment, Le Chatelier, Chatelus 
a Sauvage, chief engineer of the Lyons railroad. e useful 
effect observed in this experiment was about 9 per cent. 
