Seem eae CE is ed) de 
H. A. Rowland—Absolute Unit of Electrical Resistance, 331 
Ift¢ and 7 are the depth and width of each coil, the total 
value of M will be, when A=a nearly, 
1 | d?M d?M 
M=Moti | Gantt geet f ete 
and we find 
d? 
a ri 4 E(c) 4b7c* pm ie 
dat =~ 34 aati OA Ro" hp s ) 
F(c) (c+ 
@M, _—- xe : 
db? ~ A(1—c’) 
6? c? ; 
F(o)(2U—-e8)— gare ))— 
1—c?-c4 
B(o)(2—e8 eto mety t 
Corrections. 
Calling # and 6 the scale deflections corresponding to tan a’ 
and sin 40’, we may write our equation for the value of the 
resistance 
p) +4(5) 
1-(£) "445 
; K tand 6 (5 D 
=Ttan a 6 d\? G\:U+A+ ete.) 
1—35(5) +'22(5 
where R’ is the resistance of the circuit at a given temperature 
17-0° C., and K=20ME 14 a+b-+ete.) i ahah hy BD, ole. 
and a, b, ete. are the variable and constant corrections respec- 
tively. 
a. Correction for damping, 
a=—sA+4,A°. 
R 
b. Torsion of fiber. ne 
The needle of the tangent galvanometer was sustained on a 
point and so required no correction. e co 
torsion in the other galvanometer 1s the same for # and 6 and 
hence only affects ‘T. Therefore, if ¢ is the coefficient of 
ie b= —Ht. 
ce. Rate of chronometer. : 
Let p be the number of seconds gained in a day above the 
normal time 
e=—+_. 
86400 : 
d. Reduction to normal meter. The portion of this Sai 
tion which depends on temperature must be treated under ih 
variable corrections. Let m the excess of the meter u 
above the normal meter, expressed in meters; then 
| d=+m. 
