140 _ Dr. C. Chree on the Law 
magnetic axis and the normal to the attached mirror (see § 24). 
This does not seem, however, to be the true explanation, as 
may be seen from the following results. The notation is the 
same as in § 24; A refers in each case to the deflecting, X’ to 
the deflected magnet. 
TaBLE XVII. 
Ss Deflected é. X. True formula for P(A, X’). | 
magnet. magnet. 4 / 
: =| —— ——-——_— | 
| AN Na — 60 | +25 22-2996 2 
oon AN 193 | 85 1:999\2—2°987\2 | 
oye Ne fey AQ a 2-2-9962 
era AN 193 |. +61 D2 2-985 X!2 | 
l) Na Ne + 49| +485 19962-29952 
| Ne Na EBD | et 1-999\2—2:998 X/2 | 
The differences from the normal form 2A?—3NX” are too 
trifling to be of real moment, and have been neglected in the 
subsequent calculations. 
The second set of magnets were also mirror magnets, No. 60 
by Elhott Bros., Nos. 188 and 140 by Dover. 
Observations were made at two pairs of distances 18 and 
24 cms., and 22°5 and 30cms. The dimensions of the magnets. 
were as follows, all in centimetres. 
TABLE XVIII. 
Magnet ......... AM, -} Na. | Ne. | 60. | 138.) 140. | 
Peek tone. en| 760 | 760 | 760 | 6885 642 | 6385 
External diameter2a...) °725 ‘76 aft (ay | eee | "82 | ‘81 
Internals 4. See aa egg so) -205 | sah dine | 
The diameters appeared in all the magnets to be very 
nearly uniform throughout the entire length. 
§ 27. Some fifty deflexion experiments were made by the 
Chief Assistant of the Observatory Department, Mr. T. W. 
Baker, of whose observational skill I was fortunately able to 
avail myself. The results appear in Table XIX. X, refers. 
to AN or 60, A, to Na or 138, A; to Ne or 140. 
