470 
Cot v tan Sern WG ae 
MR JOHN ALLAN BROUN ON THE BIFILAR MAGNETOMETER, 
AW Aa 
Al 
aztAa 
re 
or, since A v is always small = 7 a, where a is the arc value of one division of 
the scale, and 2 the observed number of scale divisions of deflection, then 
acotvy=k= 
AW 
Aa Al 

n (W= AW) 
n (aeaAa) nl 
To these methods may be added that given by Gauss, depending on the time 
of vibration of the magnet. 
10. The following table contains a summary of the results for the value of k 
obtained for different bifilars by the processes indicated above. 
TABLE I.—VALUES OF THE BIFILAR UNIT CoBFFICIENT & BY DIFFERENT METHODS. 

No. Date. 

1 | May 1847, 1 

2 | Oct. 1852, { 
3 | Sept. 1854, | 
4 | Dec. 1854, 
Sept. 1854, { 
6 Nov. 1854, { 
7 Dee: ASnds { 
8 | May 1855, { 


Instrument. 

Grubb’s bifilar, Sil- 
ver wires, 
Grubb’s bifilar, Sil- 
ver wires, 
Grubb’s bifilar, Pla- 
tinum wires, 
Idem, : 
Adie’s bifilar, No. 3, 
Platinum wires, 
Adie’s bifilar, No. als 
Platinum wires, 
Adie’s bifilar, No. 3, 
Platinum wires, 

Adie’s bifilar, No. 1, 
Platinum wires, 

AO eo —_a.—— aoe Oooo ae ee 



Method. 



Deflections 3 dist. 4 in. magnet, 
” ” 15 ”? 
Comparisons with Unifilar force inst., 
Angle of torsion, 
Weights AW = +33-0 grains, 
wee (AW = + 10571.s 4: 
OAS SAS rent 
eo WN Wee eee 
Intervals A a = +0°010389 in., 
- Aa = —0-01039 
Deflections 3 distances, 
Deflections, 3:125 feet, 
2-625 
2°125 
”? 29 
” ”? 
Weights AW = —72:0gr. and + 100 gr. 
Angle of torsion, 
Deflections 3 Ainiacase 
Deflections 3 distances, 
Angle of torsion, 
Weights A W = 
Angle of torsion, : 
Weights: AW == 41:5 gr. 
Deflections 3 distances, 
Angle of torsion, 
Deflections 8 distances, 0 
Weights AW = —34°8 a and + 380 Br 
Angle of torsion, 
arora ie eomes 
= 20 Cade 
—————-s 

Coefficient 
k 
0000 (prefix). 
1351 
1356 
1353 
1251 
1365 
1367 
1370 
1368 
137 
124* 
1369 
1503 
1503 
1503 
1505 
138 
1503+ 
0578 
0574 
0700 
0692 
0513 
0510 
0501 
0451 
0451 
0449 
0436 
No. 1, Makerstoun’; Nos. 2 to 7, Trevandrum Observatory; No. 8, Agustier Malley 
Observatory, Ghats of Travencore. 
weight suspended 
2200 gr. 
6354 or.; 
No. 2, weight suspended 8491 grains ; 
No. 5, weight 2960 gr.; 

* The wire was found to shift in the groove of the suspension screw. 
j The whole instrument had been turned into different azimuths since the preceding determinations. 

Nos. 3 and 4, 
Nos. 6, 7, and 8, weight about 

