xxxvill INTRODUCTION TO THE MAKERSTOUN OBSERVATIONS, 1845 AND 1846. 
The horizontal screw was now turned in two revolutions, or one revolution farther 
in than at first, when the reading was changed from — 818 mic. div. to-+ 1120 
mic. div. 
Are of vibration at commencement, 21’. Time of one vibration, 8:00. 
Finally, the horizontal screw was turned out one revolution, as at first, the 
mean reading becoming as at first + 160 mic. div., when 
Are of vibration at commencement, 32’. Time of one vibration, 8°12. 
52. These results are very consistent, and speak much in favour of the excel- 
lence of the knife edges of the axle. It is quite certain, therefore, that the varia- 
tions in the time of vibration observed in 1844, 1845, and 1846, were not due to the 
varying position of the needle, since all the observations from 1844 till 1846 were 
obtained from the needle when in positions varying less than 400 micrometer divisions. 
53. As it was believed, that during considerable disturbances when the hori- 
zontal component of the earth’s magnetism increased considerably, the north end of 
the needle might be drawn slightly out of its position at right angles to the mag- 
netic meridian, the following observations were made to determine whether such a 
result would affect the time of vibration. 
January 144 1848. The balance needle being placed on its agate planes with its 
magnetic axis at right angles to the magnetic meridian, the following observation 
was made ; position of needle, micrometer reading + 180. 
Ave of vibration at commencement 84. Time of one vibration 115-27. 
Needle vibrated excessively by a pair of magnetic scissors. 
Are of vibration at commencement 48. Time of one vibration 115-28. 
Brought a 4-inch deflecting magnet close to the side of the balance box near 
the west extremity, in order to draw the needle out of the plane at right angles to 
the magnetic meridian; after considerable vibration, always checked by changing 
the position of the deflector, the following observation was made : 
Are of yibration at commencement 3°0. Time of one vibration 115-28. 
Performed the same operation with the deflector, and again observed, 
Are of vibration at commencement 8-0. Time of one vibration 115-12. 
Now lifted the needle by the Ys, lowered it, and observed the time of vibration 
with a large are. 
Are of vibration at commencement 1000. Time of one vibration 11527. 
