312 
MR. J. C. Me CONNEL ON AN EXPERIMENTAL INVESTIGATION 
Thus, from the observed values of t, we can obtain values of P x and P 3 for each 
ring. According to one set of theories P 1? according to the other P 3 should be always 
the same. 
The observations on Plate 1 are exhibited in Table I. The first line gives the 
value of n ; the next four the observed values of the diameters taken in plane A or in 
plane B with the principal plane of the analyser in the position indicated ; the sixth 
line the result of taking the mean of the two diameters in plane A and correcting it 
for the deviation of the axis from the normal; the seventh the same for plane B ; the 
eighth the mean of the two last. The ninth shows the diminution of Pj or P 3 for an 
increase of 1' in the diameter, so as to give an indication of the probable accuracy. 
The next line gives the approximate value of (f), and the last two the values of P x and 
P 3 deduced from each ring. 
Table I. (Plate 1). 
Temp, 
Valu@ of n. 
4. 
5. 
6 . 
7. 
8 . 
13. 
18, 
iyp 
Plane A analyser \ . 
12 ° 491' 
16° 39' 
19° 17' 
21° 251' 
23° 16f' 
30° 40' 
36 9 27' 
15±° 
/ 
12 ° 48^ 
16° 37' 
19° 151' 
21° 241' 
23° 17' 
30° 381' 
36° 26' 
13p 
Plane B ,, \ . 
12° 52' 
16° 41' 
19° 171' 
21° 251' 
23° 17A 
30° 38p 
36° 25' 
1 m° 
>> 5? / * * 
12° 51' 
16° 40P 
19° 17' 
21° 24f' 
23° 171' 
30° 371' 
36° 25' 
Corrected mean plane A . 
12° 50-1' 
16° 39' 
19° 16|' 
21° 25' 
23° 17' 
30° 381' 
36° 25' 
99 99 S • 
12° 52' 
16° 41f' 
19° 171' 
21° 251' 
23° 18' 
30° 38i' 
36° 251' 
16° 
Mean corrected diameter. 
12° 51f' 
16° 40' 
19° 17' 
21 ° 251' 
23° 171' 
30° 381' 
36° 251' 
Change of P x or P 2 per l'l 
in diameter . ) 
•040 
•030 
•026 
•024 
•022 
•0165 
•014 
Approximate 0 . . . . 
4° 9' 
5° 23' 
6 ° 14' 
6 ° 55' 
7° 31' 
9° 51' 
11° 40' 
„ Pj ... ■ 
15-084 
15T81 
15-204 
15-221 
15-232 
15-272 
15'285 
| 
P 2 . . . . 
15-258 
15-290 
15-295 
15-297 
15-290 
15-309 
15-309 
The observations on the small rings of Plate 2 are exhibited in Table II. 
Table II. (Plate 2). 
Temp. 
Value of n, 
3. 
4, 
5. 
6 , 
7. 
9. 
13. 
22 ° 
21 ° 
18° 
22 ° 
20 |° 
Plane A analyser / . . 
)> )5 \ " I 
Plane B ,, / , . 
>> r> A • 
Mean diametep .... 
Approximate 0 . 
» Pi- • • • 
,, Po . . . . 
13° 38f' 
13° 361' 
13° 34i' 
13° 37' 
13° 361' 
4° 24' 
15-054 
15-220 
18° 10 ' 
18° 8 i' 
18° 7f' 
18° 10 |' 
18° 9i' 
5° 511' 
15-207 
15-293 
21 ° 161' 
21° 15' 
21° 141' 
21 ° 16' 
21° 151' 
6 ° 511' 
15-220 
15-290 
23° 481' 
23° 48i’ 
23° 48' 
23° 491' 
23° 48A 
7° 401' 
15-260 
15-311 
26° 5' 
26° 31' 
26° 3' 
26° 3' 
26° 31' 
8 ° 231' 
15-249 
15-295 
29° 581' 
29° 561' 
29° 561' 
29° 57'“ 
29° 57' 
9° 38' 
15-258 
15-292 
36° 26P 
36° 264' 
36° 25P 
36° 26'“ 
36° 26' 
11° 41' 
15-269 
15-292 
On looking at these tables we see that P x gives values steadily increasing with < j>, 
while P 3 remains very nearly the same throughout. I think that the final values of 
the diameters of the four larger rings in each table should be correct within If or f', 
while the first three should not be in error more than 1'. In Table I. there is a line 
