A. M. Mayer—Researches in Electro-Magnetism. 108 
used a current not sufficient to saturate the tube and cylinder. 
and thus his determination would be explained by Expts. 15 
to 21. 
10 ins. ero snd slit it in its whole sone = open 
inch wide. This opening could be closed at pleasant a Sas 
ing in ita iad fitting piece of iron 10 in. long. 
Hex. 22. The above tube, with the slit closed, was placed in 
the E. helix and the 400 U. C. in the W. h elix, and needle 
brought to such a position elie them that i steed at 0° 
when circuit was open or closed. Eight cells of Bunsen. T. G. 
Ex. 28. Slit opened by removing the piece of iron. The 
needle remains at 0°. TT. G. 46°. 
Expts. 22 and 23 ame sratniey times with the same result. 
In the accompanying diagrams is shown, according to the 
theory of Ampére, the pen of the circulation of the exterior 
and interior surface-currents. It is seen boa in both cases the 
interior surface current circulates in an opposite direction to the 
exterior current; and that when the tube is slit longitudinally 
the circulation is not cut off but facilitated by the joining of the 
exterior and interior surfaces. It is therefore natural to suppose 
ree on Se of this facility afforded to the circulation that 
magnetization and demagnetization will occur in the 
split t ee in the closed tube; but no difference is found in the 
- Magnetic force of the two tubes, for the loss in surface by the 
slit seems made up in the greater facility of circulation. 
I would therefore suggest that the cores of the electro- ets 
of astronomical chronographs and of telegraph instruments be of 
soft well annealed Norway iron, made into tubes having a thick- 
ness of } of their diameters, and slit longitudinally by a narrow 
opening. 
