1384 E. H. Hall—Rotation of Equipotential Lines, ete. 
APPENDIX, 
At the Philadelphia meeting of the American Association I 
stated that I had compared the behavior of a strip of soft steel 
cemented to a plate of glass with that of a similar strip fastened 
to a plate by means of aclamp. In preparing the matter for 
publication, however, I found that the test had not been made 
so carefully as was desirable, and I have therefore just repeated 
the experiment with the assistance of Mr. W. A. Stone, of the 
Harvard class of 1886. 
I shall call the cemented strip A. It has been already men- 
tioned as No. 1 in the preceding article. The clamped strip I 
shall call B. Both strips were cut from the same sheet of soft 
steel. Each is about 1-1™ wide and 3-2 long between the 
terminals of brass. A is about -011™ thick and possibly a few 
per cent thicker than B. A suffered rather more than B in 
the process of adjustment (fig. 1). 
was not only fastened to its plate with the cement of bees 
wax and resin, but was imbedded in the cement, the latter _ 
covering it with a layer probably a millimeter or more 
thickness. The plate was not placed in water for this test 
The bearing of the clamp which fastened B to its plate was 
of wood, possibly a millimeter wide, and extended nearly from 
arm to arm of the strip. To prevent any very great bending — 
each end of the strip was loosely tied to the plate with a piece 
of twine. Otherwise the strip was free and was exposed to the 
air. 
e measurements recorded below were made between five 
and six o’clock, January 17th. There was an interval of one 
minute between successive readings of the Thomson galvan0 
meter. No measurement of the intensity of the magnetic field 
was made. It is assumed that this intensity during the one 
trial of A, which was made between the two trials of B, wa 
equal to the mean intensity during these two trials. 
The signs + and — refer to the direction of magnetization, 
R and L to direction from the zero point of the Thomson gal- 
vanometer scale. The zero position of the index in these 
experiments was a considerable distance to the right of the 
zero of the scale. The tangent galvanometer measured the 
direct current through the strip. 
Thomson Galy. Tangent Galv. 
74°0 
a 73°9 
53 R 0 73°7 
Strip B. 52 “ 3R 73°7 
Ske 73°6 
52 — 15% 505 73°8,tan, = 3°44 
