452 H. A. Rowland—Studies on Magnetic Distribution. 
In adapting the formula to apply to the case of Table I, 
we may assume that at the end of the bars = oo and C= 0, 
which is equivalent to assuming that the number of lines of 
induction which pass out at the end of the rod are too small 
to be appreciated. 
In Table IT. observations were not made over the whole length 
of the rod, and the zero-point was not at the end of the bar. 
It is evident, however, that by giving a proper value to s we 
may suppose the bar to end at any point. As the rod is very 
long, expressions of the form 
Q’—C” = C'e-*—0" and Q’e = r0'e* 
will apply. 
TaBLE IT. Bar ‘39 inch diameter. 0 at 1 inch from helix. 
v ee Q’e. Q’—o”. Q’—C”. Z F 
L. Ob- Caleu- arate of Ob- cu "’. . 
served. | lated. Q’:- served. | lated. i 
0 2 toe a Pics 902°5 
1 TET 70°8 — 9 825°2 825°9 +7 
2 65°2 65°3 + ‘1 753°5 75571 +1°6 
3 59°5 60°2 + 7 688°3 689°8 +15 
4 53°5 65°5 +2°0 628°8 629°5 + 7 
5 Si? 51°23 0 575°3 574°3 1:0 
6 46-7 47°2 + 5 524°1 §23°1 —1°0 
7 43°2 43°5 + °3 477-4 476°0 —]°4 
8 “0 40°1 + *] 434°2 432°5 —iT 
9 Ey i 37:0 — 2 394-2 392°5 Lt 
10 34:7 34°] "6 357°0 3006 — 4 
ii 31:7 3174 — °3 322°3 321°5 — ‘8 
12 29°5 28°9 — 6 290°6 290°1 — ‘5 
13 25° 26°6 + 9 261°1 261°2 4 
rf 14 25°5 24°6 — 9 235°4 235°5 — 9 
15 22°0 22°% + 7 210°9 209-0 + 1 
16 215 20°9 — 6 187°9 187°3 — ‘6 
17 20-0 19°3 — 7 166°4 166°4 0 
18 19-1 17-8 1:3 146-4 147 +7 
19 32°5 S15 —10 127°3 1294 +2°1 
21 27-5 26°7 8 94-8 97° +3 
23 23°0 22°8 — 2 67°3 pa ie 8 
25 18°5 19°4 - s z 48°6 +43 
ay 145 16°5 +2-0 25°8 29°0 +3°2 
13 14:0 +2°7 bee, 12°6 +1°3 
31 eres fe’! 1°2 
Q’—C” = 983e—%81351 89-5 — 983(10)—™-—80°5. 
Q’e = r983e—1H5L AT, — 80(10)—353LAL, 
In Table II. the observations were near the end of the rod, 
and were repeated several times. Neglecting the end of the rod, 
we haves=o. 
In these tables we see quite a good agreement between theory 
and observation ; but on more careful examination we observe @ 
certain law in the distribution of errors. Thus in Table L the 
