J. Nickles on the Permeability of Metals to Mercury. 107 
: The following are the dimensions of this electro-magnet, (see. 
gures. ) 
Length oom 
(1 ie (74 
Millimetres, Inches. 
Height ato c = 0-08 ss 3:144 
Length 610° 6 = 0-10 = 3:°937 
Thickness of n = O-OLL cs 0-432 
- a a 0023 = ‘903 
= ns 2-633 
om) 
— 
=) 
a) 
| 
n : 
It is clear that by putting plates of iron on the two free sides 
and fixing over the polar surface a plate of steel so as to inclose 
the whole, the copper wire would be as completely protected as 
possible against every species of accident. The electro-magnet 
may be exposed to all kinds of danger without fear of injury, and 
in this State may be used as a brake ou railroads to stop the spee 
or motion of the cars. 
Strength of the other, and the reverse. igs 
Arr, XVIIL—On the Permeability of Metals to Mercury ; by 
i gan M. J. Nicxiss.* 
In an interesting memoir on the permeability of metals to 
meteury, by Prof. Horsford, this author establishes the fact of the 
Petmeability of tin, lead, gold, silver, zinc, and cadmium, aud 
Contests that of copper aud brass. 
The negative results which this chemist has obtained with 
“oppet and brass, have evidently proceeded from the process 
Which he has followed: for, some time since while engaged 
in tay researches on magnetization, I observed positive facts to 
with tary. 1 was using at this time a Bunsen’s battery, 
Fw exterior. The connecting pieces of copper were 
‘ to the zinc; and on amalgamating the latter metal, it 
2 ten happened that the mercury spread itself over the copper 
contact with the zinc: and after a certain time, the met 
~ * Communicated by the author in French for this Journal. 
