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H. A. Rowland— Absolute Unit of Electrical Resistance. 3385 
and 11:5 seconds. They were suspended by three single fibers 
of silk about 48 em. long. 
In front of the needle was a piece of plane-parallel glass. 
This and the mirrors were made by Steinheil of Munich, and 
were most perfect in every way. 
In the winding of the coils every care was taken, seeing that 
a small error in so small a coil would produce great relative 
error. And for this reason the constant was also found by com- 
parison with another coil. The following were the dimensions: 
Mean radius 4°3212 c. m. 
212 r= 30212 
X=3°475565 w= “935565 
R-r=2°6000 X—wr=2°54000 
N=1790° 
whence 
F=1832-25—1-70 52Q, (0) —4°50 b4Q, (A)+ 90 5°Q, (0) — &e. 
Taking the mean dimensions of the two needles, we have 
1=1°23, w='52, n=}, cosi’=748. 
Q,(4)=+'339, Q,()=—354, Q,(W)=— 275. 
.. G@=1832°25—"083-+- 071 — 002 + &c.=1832°24. 
The coil with which this galvanometer was compared was 
the large coil of an elec ynamometer similar to that de- 
scribed in Maxwell’s “ Electricity,” Art. 725, but smaller. The 
coil was on Helmholtz’s principle with a diameter of 27° cm., 
and was very accurately wound on the brass cylinder. There 
was a total of 240 windings in the coil. The constant of this 
coil was 78-371 by calculation. 
T’o eliminate the difference of intensity of the earth’s mag- 
netism, an observation was first made and then the positions of 
the instruments were changed so that each occupied exactly 
the position of the other: the square root of the product of the 
coils together and the other with them separate. The results 
were for the ratio of the constants 
23'3931 and 23°4008, 
which give 
G=1833°37 and 1833°98. 
The mean result is 
1833-67 - °09, 
and this includes seven determinations with two reversals of 
instruments. This result is one part in thirteen hundred 
greater than found by direct calculation, which 
accounted for by the small size of the galvanometer ¢ 
is to be 
oils and 
