616 Proceedings of the Koyal Society of Edinburgh. [Sess. 
Tensile Strengths of the Steels . — With a view to obtaining complete 
information relating to the steels, it was decided to determine their tensile 
strengths in the annealed condition. Specimens were accordingly prepared 
and pulled out on a Wicksteed ten-ton testing machine. The results are given 
in Table II. 
Table II. — Tensile Strengths of the Steels employed. 
Description of 
material. 
Breaking stress 
in tons 
per square inch. 
Ultimate percentage 
extension on a 
length of 4 inches. 
Percentage contraction 
in sectional area 
at fracture. 
Mild steel . 
26-3 
24-0 
67-0 
Spindle steel 
53*4 
8-0 
18-0 
Steel wire . 
70-0 
9-0 
10-0 
Magnet steel 
57-6 
6-4 
11-0 
Special hard steel 
70-8 
7-5 
4-0 
1 
The above figures are the means of tests carried out on two specimens of 
each variety of steel. The results agreed closely with one another. 
Effect of Vibration . — In the previous part of this paper it was men- 
tioned that the “ sensitive state ” could be greatly reduced by jarring the 
specimens. This effect has now been much more fully investigated. The 
method adopted in the preliminary experiments for vibrating the specimens 
has been in the main adhered to, but important alterations have been intro- 
duced in the minor details. It was found in the case of those specimens 
which were dropped vertically several times on the stone slab that a con- 
siderable amount of permanent magnetism was built up if the same end 
was lowest in each fall. The amount so induced was sufficient to affect 
the subsequent tests, which were confined to small magnetising forces. 
Dropping the specimen on either end alternately would have avoided this 
gradual augmentation of permanent magnetism. The procedure is, however, 
objectionable, in that it results in the specimen being subjected to an 
alternating magnetic field which, though of small intensity, would diminish 
the “ sensitive state ” for much larger values of H, as has previously been 
shown by the authors. The following method was therefore devised and 
adhered to. A solenoid of insulated copper wire was wound over a brass 
tube about 130 cms. in length, and the arrangement mounted vertically, 
with its lower end resting on the stone slab. With a view to avoid jarring 
of the specimens subsequent to their fall, the tube was lined with felt. A 
current was passed through the solenoid of such strength as to exactly 
neutralise the vertical component of the earth’s field. The specimen was 
then dropped in the tube through a distance of 1 metre on to the stone slab. 
As there was no magnetising force to influence the “ sensitive ” condition 
