xl INTRODUCTION TO THE MAKERSTOUN OBSERVATIONS, 1845 AND 1846. 
that this effect is nearly constant, while the time of vibration in the vertical plane 
has varied from upwards of 11 seconds in 1843, to less than 6 seconds in 1846 
(No. 77, 3d); the differences of the results for the temperature coefficient being in 
all probability due to considerable changes of vertical force in the periods selected 
for the determinations, and certainly having no relation whatever to the varying 
time of vibration. Since the temperature coefficient in micrometer divisions (q’) 
has remained constant, it follows that the coefficient of reduction (/) must also be 
constant. This conclusion renders it the more desirable that the value of the angu- 
lar motion of the needle in parts of the vertical component should be determined by 
another method which does not involve the time of vibration; the statical method 
already described for the bifilar magnetometer, has been employed for this purpose 
with some modification. 
58. January 6, 1848. Wooden beams having been placed horizontally at right 
angles to the magnetic meridian, and a line having been drawn upon them, which 
was a projection of the prolongations of the balance needle, a small deflecting bar 
(3°65 inch long, and having a temperature coefficient = 0-000285), was placed verti- 
cally at different distances on the beam, and the angles of deflection of the needle 
were observed ; the centre of the deflecting bar was in the prolongation of the axis 
of the balance needle when horizontal, and the distances were measured from the 
knife edges of the axle, which, however, was found not to be the centre of magnetism 
of the needle. The resulting deflections and values of & for each distance will be 
found Table 5. 
January 10, 1848, the balance needle was taken out of its box, and attached to 
the brass detorsion bar of the declinometer ; the brass bar was mounted with a glass 
seale and lens, and was suspended in the declinometer box ; the balance needle was 
then deflected by the bar used for the previous deflections, which was placed to the 
north and south of the suspended needle, so that in both series of deflections the 
prolongation of the balance needle in its normal position passed through the centre 
of the deflecting bar. The deflections for three distances are given, Table 6. 
TABLE 5.—Observations of Deflection of the Balance Magnet resting upon the 
Agate Planes, January 6, 1848. 
iF | i] 
| Bar B. Bar W. 3 Bar W. | 
Order | 
Dis- | 75 sal nF N. end i aed N. end | Deflec- 
ong Obsor: Tea ray eee (ech et aL See -_ ll Obser- |__down- amet | ti S,. || Value of &. 
a. 
| 
vation. | Balance. || vation.| Balance. || vation. Balance. vation. | Balance. 
| | 
| 
| 
Mic. Div. | Mic. Div Mic. Div. Mic. Diy. | Mic. Div. | Mie. Div. | 
+ 36-7 4 19-E — 49-0 | | 
+ : 38: — 201-5 — 382-2) 308-5 | 309-0 | 7.94533 || 0-0000099 
+ 282.0 — 479-7) 391-7 | 392-3 | 8-06003| -0000099 
+ 444. 32. 401-2 |— 625-5) 525-7 | 506-5 || 8.18828) -0000099 
+ 375-5 | — 583-5 3 |— 850-5 730-4 | 731-5 | 8-33067)) -0000099 
+ |— 890-0 |) — 1227-0 1065-7 | 1067-4 | 8-49577 | -0000099 
+ ~ 1125.0 — 1505-5 | 1328-9 | 1331-0 | 8-58925 |) -0000096 
1 
2 
3 
1 
5 
6 
7 
— 44-5 | | 
— 280-7 — 349-5) 289-6 | 290-1 | 7-94533 | 0-0000101 
+ 899-0 9 |+1172-0 — 912-5 — 1188-0) | 1045-4 | 1047-5 || 8-49577 || -0000103 
| | 
