102 A, M. Mayer—Researches in Hlectro-Magnetism. 
mained at 0°. On further decreasing the thickness the : send 
of the needle was deflected toward the W helix. TT. G. 4 
It thus appears that a tube of this size having a elape of 
2 of its diameter is, Sy magnetized with this strength of cur- 
rent (8 cells, T. G. 4 46°) equal in effect to a solid cylinder of 
the same diameter, 
x. 14. Another tube was constructed having a diameter of 
13 in. and a thickness of } the diam. Into this tube slida 
solid core. Placing the uninsulated wire-core of 400 in 
lix and tube with inner core in E. helix, the needle was placed 
so pana it stood at 0° when circuit was open or closed. TT. G. 
46°. 
Ex. 15. Withdrew inner core. Current passed. S. 40’ W. 
T. G. 46°. Thus a tube of the above diameter, having a thick- 
ness of } of its diameter is not equal to a similar solid cylinder. 
This subject will therefore have to be the object of further in- 
vestigation. 
Thinking that in the case where a current did not saturate 
the above tube it ~~ equal the solid cylinder, the following 
experiments were m 
. The rabe used in (14) was placed with inner core 
in EH. helix, and a similar tube and core in W. helix, and the 
needle placed so that it stood at 0° when cireuit was open or 
closed. A current from 4 cells was passed. G. 32°. 
ul 
Fx. 17. Solid core removed from tube in helix E. Needle , 
remains at 0°. Hence for this strength of current (T. G. 82°) 
the tube is equal to an equivalent solid a nder. 
fx. 18. Other things remaining as in (17) a ‘current from 5 
cells, T. G. 37°, was passed through helices. Needle 8. 2’ W. 
= 19. Current passed from 6 cells. T. G. 40°. Needle 8. 
15’ W. 
Fx. 20. Current passed from 7 cells. T. G. 42°. Needle 
S. 20’ W. 
Fx. 21, Current passed from 8 cells. T. G. 44°. Needle S. 40’ 
W. Itis clearly seen from above experiments that with a current 
of T. G. 32° the tube is 92 ual to the similar solid cylinder, but 
on erally pen e current up to T. G, 44° that the 
tube falls more and more below the strength of the cylinder, 
and the pees is again deflected S. 40’ W. toward the cylinder 
with that current. Therefore in determining what portion of 
the interior of a cylinder can be vemoved so that what remains 
equal the solid cylinder we should see that the tube is 
“saturated,” otherwise the comparison does not solve the prob- 
lem. ee this condition was fulfilled in Expt. 13 was not 
ascertain 
In Daguin’s Traité de Physi vol. iii, p. 615, Paris, — 
we read: “M. Du Moncel ea tty hace, te er 
i isi, i > * 
| pene 
4 
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