TBA Dr. C. Chree on the Law 
When the magnetic moment is 1000 ¢.G.s., 22°5 cms. is 
too short a distance unless H exceeds :185. 
Tanta Vil, 
Error of 1/ in deflexion-angle. Effect on H (unit ly). 
Observations at two distances, Q negligible. 
H m | Distances 225 30 | 25 35 | 26:25 35 | 30 40 | 35 45cms. 
C.G.S. C.G.S.| Sign ...... +-)/+ -) 4+ -|)/+ -) + = 
ape ees ve | 29 I) 46 23-6) 7-9 35°9/158 570 
750) «es 34 193) 46 285 69 S19 110 481) 24 768 
ao fang Aree 128 60 152 86 221 97 (339145 | 
7 Na oe 182 81 209116 30:1130 (456194 | 
/ 
| 
Taste VILLI. 
Error of 1’ in deflexion-angle. Effect on H (unit ly). 
Observations at three distances, neither P nor Q negligible. 
pen ee sss —_————. | --- an —_—~ 
ae oN 
H m | Distances 225 30 40 | 25 35 45 262535 45 | 30 35 40 
| 
C.G.S. 0.G.S. Sign ...... - + - + —- + —-|j;—- + = 
185 .{ 1000). ---sscs.s me | 13 32 82] 24 36 86/ 22 127 153 
Tai , seks 16 25 70) 2:1 44110] 36 49 116 | 30 172 205 
| 
gig [208 peel 59 77 212 | 68132 332 11-4148 348 | ... 
Allens oe ae 8-4 104 283 | 93177 442 155198 464 |... 
As an illustration of how to read the Tables, suppose that 
when a deflexion is made at 30 cms. with a magnet of 
moment 750, at a station where H is *185, the angle is taken 
1' too high; then the error in the value calculated for H is: 
—8'5y when P and Q are negligible, and the 30 cms. obser- 
vation is alone used ; 
—19°5y when () is negligible, and observations are taken at 
30 cms. and 22°5 cms. ; 
+11:0y when Q is negligible, and observations are taken at 
30 cms and 40 ems. ; 
4+25y when neither P nor Q is negligible, and observations 
are takenat 22°), 30, and'40 cms.; “(Suita 
—30y when neither P nor Q is negligible, and observations 
are taken at 30, 35, and 40 cms. 
So long as the errors are small, the effect on H is propor- 
tional to the size of the error, and the results in Tables V1., 
