PROFESSOR KEELY’S RIAGNETICAL OBSERVATIONS. 
209 
cient of magnet H(10) ; 
^ y,2^5 gjjj gjjj y 
and Table VI. shows the values of P from the formula 
using the distances 1 foot and P4 foot. 
Table VI. 
Lamont’s method was adopted of obtaining the moment of inertia of cylinder H(10) 
by means of a brass ring accompanying the instrument, whose dimensions were, — 
ft. 
External diameter . . 0‘2153'| 
Internal diameter . . 0T667 p Whence log A;'='5489695. 
Weight* J 
The cylinder H(10) had on it, at the ends, two small brass rings, the contour of 
which I shortened by filing, so as to bear conveniently the metal ring in vibration. 
Twenty-one sets of vibrations without the ring, and eight sets with it, made between 
the 2nd and 6th of October, varying, in number of vibrations, from 340 to 466 each, 
and corrected for temperature, arc, torsion and rate of chronometer, all observed 
at the same times, gave for log at a mean temperature of 63°-3, 1-3320923. 
Observing, however, that the cylinder suspended seemed very slightly depressed at 
the N. end, I shifted the little ring there to the S. end, putting it in contact with the 
other ring, and at such a distance from the end of the cylinder as I had calculated 
would give the same moment of inertia ; and then on the 8th and 9th of October 
made more observations for the particulars of which are in Table VII. 
Date. 
Values of P. 
July 28. 
July 29 . 
Sept. 25. 
Nov. 27 . 
Dec. 8. 
— 00042 
— 00091 
— 00157 
— 00162 
— 00102 
Mean ... 
— 00111 I 
Table V. 
April 29 th and 30th. <|^ 
•000160 
•000169 
•000158 
•000168 
Mean 
•000164 
Table VII. 
Date. Civil reckoning. 
Whole time. 
Number of 
vibrations. 
Time of one 
vibration. 
Com- 
mencing 
arc. 
Final 
arc. 
Tempe- 
rature. 
Torsion for 
90° in scale 
divisions. 
Rate 
cbron. 
k. 
d h m 
Oct. 8 9 33 a.m. 
8 10 21 A.M. 
8 01 18 p.M. 
8 02 32 p.M. 
8 03 17 p.M. 
9 01 00 p.M. 
9 01 55 p.M. 
9 02 53 p.M. 
9 03 47 
9 04 33 
1448-3572 
2091-8929 
1500- 8215 
2103- 
1490-7857 
1501- 
2217-2643 
1499-0357 
2228-8857 
1523-4785 
330 
294 
342 
296 
340 
342 
312 
342 
314 
348 
4-38896 
7-11528 
4-38836 
7-10473 
4-38466 
4-38889 
7-10662 
4-38314 
7-09836 
4-37781 
Sc. div. 
3-0 
3-0 
2- 9 
2-8 
3- 0 
2-9 
2-9 
2-9 
2- 7 
3- 0 
Sc. div. 
•4 
•9 
•7 
•1 
•6 
-7 
•1 
•4 
•9 
•6 
50-5 
54-5 
65-4 
65-75 
64-0 
59-5 
59-3 
56-0 
56-1 
50-5 
•8725 
1-1800 
-76 
1-065 
•69 
•55 
•945 
•6875 
1-0925 
•795 
// 
-6-5 
— 6-5 
—6-5 
— 6-5 
—6-5 
—6-5 
— 6-5 
— 6-5 
—6-5 
—6-5 
■ 
J 
■ 2-1743 by 1st set. 
> 2-1787 by 2nd set. 
>2-1766 by 3rd set. 
2-1764 by 4th set. 
2-1765 mean value. 
* Weight not stated in the MSS. — E. S. 
