of Action between Magnets. 121 
Tasie III. 
Values of 
| Value of 6H/H. 
r; A oe ge 
ems ems. | cms. | 
22°5 30 40 | —0:0397 67, +°1469 dr, —-1254 dr, | 
5) 35 45 —0-0279 dr, +°1340 dr, —-1220 dr, | 
26-25 35 | 45 —0:0379 ér, +°1500 67, —*1279 dr, | 
27 36 | 48 —0:0331 67, +°1224 6r, —-1045 Or, | 
30 35 | 40 —O178 or, +°528 Or, —'366 dr, | 
In Table III. the unit of length is 1 cm., the unit of 
force is immaterial. 
At a particular station it would be simplest to use an 
approximate value for H, and it might be most generally 
convenient to take °001 cm. for unit of length, and ly for 
unit of force. This is done in Table IV., applicable to a 
station where H is approximately °185 c.@.s. 
Tanne LV. 
Values of : 
——| Value of 6H. (H='185 c.«.s.) | 
ry | 73  |(001em. unit of length, ly unit of force.) | 
ems. | ems. | ems. | | 
225 | 30 | 40 | —O%odr, 4+2720r, —2°32 dr, 
25 30 45 | .-—0°52 or; +248 6dr, —2°26 dr, 
26°25 | 35 45 —070 or, +277 6r, —2:37 Or, 
| 27 36 48 | —O6lodr, +2°26 or, —193 ér, | 
| 30 | 38d 40 | —329 dr, +9°760r, —676 6r, | 
| | 
At a station where H=‘370 ¢.a.s. the coefficients of 67, 
672, Or; in Table LV. would be simply doubled. 
§ 8. If in (16) we suppose 
673/7'3 = O75/P2 = Or,/T15 ° . . . : (23) 
or if in (22) we suppose 
87/72 = 874/74, 
we alike find 
6H/H = —36r,/7,. 
Thus if all the distances have errors proportional to the true 
lengths—as might, for instance, occur through an error as to 
the coefficient of thermal expansion—the simple relation 
(21) applies irrespective of the number of points at which 
ae are made. 
