and form for a compass needle. 
12 7 
vious to the experiments they were all made red hot, to de- 
stroy any accidental magnetism. 
The compass employed was of a very delicate construc- 
tion, and the cylinder was so placed that its centre was in the 
direction of a tangent to the zero of the compass, and at the 
distance of 4,85 from -the southern extremity of the needle. 
The position of the cylinder was varied six times, and the 
following were the deviations of the needle. 
Sheet iron cy- 
linder. 
Chest plate cy- 
linder. 
Solid cylinder. 
O / 
» / 
0 / 
2.15 
2.50 
2 55 
2.15 
3- 4 
3-15 
2.45 
3.20 
2-57 
2- 5 
3-45 
2.50 
2- 5 
3.10 
2.55 
2.10 
3-3° 
2 3° 
2.l6 
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 cy- 
linder was now varied eight times. 
Sheet iron cy- 
linder. 
Chest plate cy- 
linder. 
So!id cylinder. 
O / 
O / 
O / 
2. 3 
2 -55 
3 J 5 
2.22 
2.50 
3- 12 
2.32 
3.20 
3 15 
2.20 
3-4° 
3. 0 
1 . 5 ° 
3-4° 
3*5 
245 
3.28 
2 50 
2 45 
3.10 
2.45 
i-55 
3- 5 
2.58 
2.19 
3.16 
3- 4 
Mean 
