Equipotential Lines of an Electric Current.. 437 
Appendin. 
At the Philadelphia meeting of the American Association 
I stated that I had compared the behaviour 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 a clamp. 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 
mentioned 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. Hach is about 1:1cm. wide and 3:2 cm. 
long between the terminals of brass. A is about ‘O11 cm. 
thick and possibly a tew per cent. thicker than B. A suffered 
rather more than B in the process of adjustment (fig. 1). 
A was not only fastened to its plate with the cement of 
beeswax and resin, but was imbedded in the cement,. the 
latter covering it with a layer, probably a millimetre or more 
in 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 millimetre 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. 
The 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 galvano- 
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, 
was equal to the mean intensity during these two trials. 
The signs + and — refer to the direction of magnetization, 
Rand L to direction from the zero point of the Thomson 
galvanometer-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 Galyv. Tangent Galyv. 
74:0 
+- — T3°9 
ans ihe 0 iat 
Strip B ) 52 one 
Gilesuldetok suas 736 
52 — 1:5=50°5 73°8, tan.=3°44 
