16 W. N. Hill—Electro-Dynamometer for Large Currents. 
This table shows whole webers only, which, for some pur- 
AEE would be sufficient, but the subdivisions « can be ape 
ired. Thus, we have between 59 and 60 webers 
8 w. 8. w 
webers webers er 
4°590 59°6 4°680 
591 4°605 59°7 4-700 
59°2 4°620 59°8 4-715 
59°3 4°635 59°9 4-730 
59°4 4°650 60 4:750 
59°5 4-665 
s. 
It is plain that a set of weights could be made which would 
represent webers current, making any calculation unnecessary. 
This would be often aca venient if much work was to be done. 
For technical purposes, when an approximate measure is 
sufficient, a set which would not be too cumbrous might have 
brass weights for differences of five webers, and platinum ones 
for intermediate figures. Thus, between 80 and 40 webers :— 
Principal weights. Lames weights. 8. 
grm. 30 webers. 
1 vos 2 210 grm. 
1615 1 095 35 
095 2 *195 
2-110 1 40 
With this instrument, I have worked with currents as small as 
10 webers, but it is not sensitive enough for such use. Above 20 
webers, it operates satisfactorily. Greater nicety of construction 
would sonitet greater sensitiveness to small weights, but it is 
evident that this form of the dynamometer is particularly suit- 
able for large currents. 
We have S: S's: fw: fw, 
That is, as the currents increase, the pages. peice weights 
increase more rapidly and greater accuracy and minuteness are 
attained. Between 21 and 22 webers, se diffrence of weight 
is ‘06 grm., and between 99 and 100 QT g 
My best thanks are due to Prof. eile Prowbridde of Har- 
vard University, for advice and the use of his apparatus. 
U. S. Torpedo Station, Newport, R. I., October 25, 1879. 
