828 H. A. Rowland—Absolute Unit of Electrical Resistance. 
6. aN of the resistance of German silver with the 
emaperse 
7.» Perhporabare of standard resistance. 
Arc of swing when the time of vibration is determined. 
9. Length of needle in ee and other galvanometer 
ary! compensated by the me 
Onin variation of saaietsada of circuit during the experi- 
Be 
The i i errors are compensated by the method of 
experim 
1. The Teal and daily variation of the earth’s magnetism. 
2. The variation of the magnetism of the nee 
3. The magnetic and inductive action of the parts of the 
apparatus on each other 
4. The rea for length of needle in the tangent gal- 
vanometer (nearly). 
The axial displacement of the wires in the coils for 
induction 
6. The error due to not having the coils of the galvanom- 
eter and the. circle parallel to the needle. 
7. Scale error (partly). 
8. The zero error ot pe 
Caleulation of Constants. 
Circle.—For obtaining the ratio of G to G”, it is best to cal- 
culate them separately and then take their ratio, though it 
might be found by Maxwell’s method (“Electricity,” Article 
753). But as the ratio is great, the heating of the resistances 
would produce error in this latter method. 
For the simple cir 
4 
I EE (13(5) + &e.) 
(A? 4+B2)2 A 
where A is its radius aan ~ the distance of the plane of the 
circle to the needle on its 
Galvanometer for Jue 7. the more sensitive 
its sensitiveness. If we make the galyanometer of two cir- 
cular coils of rectangular section whose depth is to its width as 
to 100, and whose centers of sections are at a radius apart 
from each other, we shall have Maxwell’s modification of 
Helmholtz’s arrangement. The oon He can then be found 
by calculation or comparison with another coi 
axwell’s formule are only adapted to coils ‘of small section. 
Hence we must investigate a new formula.* 
* A formula involving the first two We 
peci ame ot ead the cente: wo tems of my sores, but ep erie siete tion, 18 
— Elektrodynamische Maasbestimmungen inbesondere 
