xl Introduction to the Makerstoun Observations, 1844. 



51. In order to determine more distinctly whether change of inclination of the 

 magnetic axis affected the time of vibration to any considerable extent, the follow- 

 ing observations were made during an adjustment of the instrument. 



January 18, 1848. The balance needle with its magnetic axis in the magnetic 

 meridian, nearly horizontal, mean position + 160 mic. div. 



Arc of vibration at commencement, 32'. Time of one vibration, 8 S 05. 



After this observation, turned out the horizontal screw one revolution, which changed 

 the reading from + 160 mic. div. to — 818 mic. div. 



Arc of vibration at commencement, 32'. Time of one vibration, 8 s * 12. 



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. 



Arc of vibration at commencement, 21'. Time of one vibration, 8 S# 00. 



Finally, the horizontal screw was turned out one revolution, as at first, the 

 mean reading becoming as at first + 160 mic. div., when 



Arc of vibration at commencement, 32'. Time of one vibration, 8 S -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, were not due to the varying position 

 of the needle, since all the observations in Table 5, 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 14 d 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. 



Arc of vibration at commencement 8'"4. Time of one vibration ll s -27. 



Needle vibrated excessively by a pair of magnetic scissors. 



Arc of vibration at commencement 4'*8. Time of one vibration ll s 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 



