18 Lovering and Bond on Magnetic Observations at Cambridge. 
mean of the partial results, so that the latter column in the table is 
unnecessary and a great part of the labor of reduction is saved. The 
number 12 is a convenient divisor, and after the whole minutes are 
found the decimals are taken out of a Table calculated for this pur- 
pose and embracing every case that can occur. Look in the verti- 
cal column at the right or left for the whole numbers of the remain- 
der, after dividing by 12, and in the top or bottom line for the 
eights, and in the corresponding square is the decimal value of the 
remainder. 
| 
to -|¢| 
AIT | 427 | 437 | 448 | 458 | 469 | 479 | 490 | 
573 | 
583 | 594| 604) 615 | 625 | 635| 646 |656| 7 
667 | 677 | 687 | 698 | 708 | 719 | 729|740| 3 
750 | 760 | 771 | 781 | 792| 802| 812/823; 9° 
"833 | 844| 854 865 | 875 | 885 | 896 | 906 | 10 
17 | 927 | 837 | 948 | 758 | 969 | 979 | 990| 11 
O | ie Cts ars rien hee 
or 
(=) 
io) 
Or 
Se) 
on - 
wo 
—_ 
on 
iv) 
oO 
ai 
iS) 
a 
or 
iS) 
oO 
(op) 
to 
a 
° 
co 
ie) 
a) 
| 
_ 
_ 
ido) 
| 
It must be observed that the mean result obtained above corre- 
sponds to 3° 39” 59”.5, and not 3" 40’. ‘But the difference of 
half a second comes within the limits of unavoidable errors of 
observation and is of no weight in deciding on the comparative 
merits of the two methods each of which depends on a knowl- 
edge of the time of vibration of the bar. But this time changes 
slightly from one period to another, and although always assum- 
ed to be 54” it is strictly 53’.4 on the average, and oscillates 
