by the expression D 
Equipotential Lines of an Electric Current. 
425 
M means intensity of magnetic field perpendicular to plane 
of paper in fig. 1. 
R. P. means rotatory power, which is numerically defined 
Cx MW’ 
in which D is the thickness of 
the metal strip, and E is the electromotive force resulting 
from C and M which maintains the transverse current*. 
The R. P. is considered positive when E is of such a character 
as to send a positive transverse current in that direction in 
which the conducting strip tends to move under the action of 
the main current and the magnetic force. 
The temperatures referred to in the tables are those indi- 
cated by a thermometer placed in the water-tank containing. 
the plates when under examination (fig. 2). 
Copper, Zinc, and their Alloys. 
Composition | _ Composition, | 
ace. to Pit ER | &e.t 
s, | chem. anal. | ies Near | 
e Date. Temp.| M.| C. 1013 | 24° 0 
| 2 | Per | Per | Pe FO a Per “ieee | 
cent. | cent. cent. | cent. | 
| Coppr.| Zinc. | Coppr.| Zinc. | 
| (| 100 | 1888. | °C | | | 
| | (99-9) | Aug. 11} 8 |5700|-0619 | (—521) | | | 
<a Gene |» | 48 (5640! -0819 | (—530) | | 
| ee | ,, | 21-5 |5560) -0876 | (—520) | | (—520) | 
| 4 haar | Aug. 29 | 24-5 |6080! -1906 | (—519) [|S °°? | | 
| | 
B { 81:3 | 18-7. | | | | | 
(81-08)|(18°51)| Aug. 18 25 [5750'-1800 | (—404) |(—404) | 913 | 87 | 
| 73 | 27 | | | | | | 
C4 |(72:86)\(27-02) Aug. 17| 5:1 5€80,-1810 | (—246) | | 
: a » | 22°8 |5700| -1830 | (—250) |(—250) | 80 | 20 
(| ez | 33 kort ¥) | | 
D4 |(66 85)\(33-04) Aug.13 6 {5830-1680 | (—178) | | | 
| | n x ~~» | 25-~—«*(5980| 1680 | (—166) | (—166) | 73:6 | 26-4 
| / | / | \ | 
) 6 94 | | / 
| F4 | (5-87)|(93-79)| Aug. 17| 4  |5640|-1790 | (+527) | 
| . » | 9» | 242 15690}-1'780 | (+496) | (+496) | 24:3 | 75-7 
| 0-0 | 100 | er er | | 
g || (trace)|(99'54) Aug. 15/44 (6150 -1860 | (+838) _| | 
|» | 224 6210-1870 | (+809) ~— 
; prea : ean MES 
* The R. P. of this article is the reciprocal of the quantity E used 
in my article in this Journal for November 1880. 
+ Composition of alloys which @ prior: might have been expected to 
have these values of R. P. 
