J22 Dr. C. Chree on the Law 
§ 9. The corrections 6P, 6Q to the values of P and Q, 
when corrections 67, 57, 673 are applied to the distances 
71, Y2, 73 at which deflexions are made, are given in Table V. 
for the same combinations of three distances as appear in 
Table IV. 
TABLE V. 
(Unit of length 1 cm.) 
r ek oP. 10-° 6Q. 
22:5 | 30 | 40 — 198ar, + 619 dr, — 358 dr, | 114 ér, — 23887, +114 dr, 
25 | 35 | 45 |— 181 dr, + 710dr, — 452 dr, | 188.ar, — 339 dr, +187 ar, 
26-25 35 | 45 — 246 dr, + 814ér, — 490 ar, | 188dr, — 419 dr, +216 or, 
27 =| 86 | 48 |— 238 dr, + 743 dr, — 423 dr, | 197 br, — 411 dr, +197 dr, 
30 | 35 40 —1006 dr, +2638 dr, —1554 dr. | 698 dr, —1520 87, +806 dr, 
Here again we see the large effect of even small errors in 
the three distances when the intervals are only 5cms. When 
7;/2=12/r3=3/4, the coefficients of dr, and dr, in the ex- 
pression for 6Q are absolutely equal. 
A check on the results in Table V. and analogous Tables is 
supplied by the fact that if 
or, /7,= 672/73 — 873/7°s, 
then we ought to have 
sP-=0= 80, 
This is obvious from the general formule (i7) and (18) 
applicable to three distances (and it is equally true for 
deflexions at two distances only, when Q is negligible, though 
this case is not covered by Table V.). 
Additional interest attaches to this simple result from the 
fact pointed out in a recent paper *, that in ordinary English 
magnetometers the increments in the distances 7; &c. due 
to bending of the deflexion-bar are nearly proportional to 
the distances themselves. The neglect of the bending effect 
thus entails fortunately but little error in the determination 
of 2yor, Q. 
Effect of Errors in Angles. 
§ 10. When a small error—whether due to reading or, to 
defective graduation—has been made in a deflexion-angle wu, 
the consequent small error 6H is given by the following 
formule :— 
* Phil. Mag. Jan. 1904, p. 39. 
