372 On the best Kind of Steel and Form 
face. For this purpose I had three cylinders made of soft iron, 
about two inches and a half in diameter, and nearly the same in 
height. One of the cylinders was of sheet-iron less than the 
20th of an inch in thickness; the second of that kind called 
chest plate, 0-185 inch thick ; and the third was of solid wrought 
iron. The first weighed 2760, the second 9376, and the solid 
cylinder 22929 grains. Previous to the experiments they were 
all made red-hot, to destroy any accidental magnetism. 
The compass employed was of a very delicate construction, 
and the cylinder was so placed that its centre was in the direc- 
tion of a tangent to the zero of the compass, and at the distance 
of 4°85 from the southern extremity of the needle. The posi- 
tion of the cylinder was varied six times, and the following were 
the deviations of the needle: 
Sheet iron Chest plate Solid 
cylinder. cylinder. cylinder. 
215’ 2° 50’ Jai 
215 3.4 3 15 
2 45 3 20 2 57 
2’ 3 45 2:50 
2.5 3 10 2 oo 
2 10 3 30 2 30 
Mean .. 2 16 3 16 2 54 
Suspecting an error in the experiments with the solid cylinder 
from an accident which occurred, I repeated the whole with the 
utmost attention. The position of each cylinder was now varied 
eight times. 
Sheet iron Chest plate Solid 
cylinder. cylinder. cylinder. 
2° 3 2°55 3°15 
2 22 2 50 rf ak ee 
2 32 3 20 3.15 
2 20 3 40 — 3 0 
1 50 3 40 315 
2 45 3 28 2 50 
2 45 3 10 2 45 
1 55 35 2 58 
Mean .. 2 19 3 16 3.4 
The surfaces of the cylinders determined by very careful mea- 
surement were, the sheet iron, 28°54; the chest plate, 30°77 ; 
and the solid cylinder, 28-94 inches, 
Reducing the deviations to the same extent of surface, viz. 
that of the solid cylinder, they become respectively 141, 184, and 
184 minutes,. 
These 
