xl Inteoduction to the Makerstoun Observations, 1845 and 1846. 



that tliis 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 (k) 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 bi filar 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 k 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 

 scale 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. 





Order 



Bar E. 



Order 



Bar W. 



Order 



Bar E. 



Order 



Bar W. 











Dis- 



of 



N.end 



of 



N. end 



of 



N. end 



of 



N.end 



Deflec- 



Deflec- 



Log. 

 tan. u. 





tance of 

 Bar. 



Obser- 

 vation. 



up. 



Obser- 

 vation. 



up. 



Obser- 

 vation. 



down. 



Obser- 

 vation. 



down. 



tion at 

 37°. 



tion at 

 32°. 



Value of k. 



Balance. 



Balance. 



Balance. 



Balance. 



Feet. 





Mic. Div. 





Mic. Div. 





Mic. Div. 





Mic. Div. 



Mic. Div. 



Mic. Div. 







Away 



1 



+ 36-7 



14 



+ 69-5 







27 



- 49-0 





' 







2-6 



2 



+ 267-0 



1 1^ 



+ 383-5 



15 



- 201-5 



26 



- 382-2 



308-5 



309-0 



7-94533 



0-0000099 



2-4 



.3 



+ 3.33-5 



' 12 



+ 471-5 



16 



- 2820 



25 



- 479-7 



391-7 



392-3 



8-06003 



-0000099 



2-2 



4 



+ 444-1 



i ^^ 



+ 632-0 



17 



- 401-2 



24 



- 625-5 



525-7 



506-5 



8-18828 



-0000099 



20 



5 



+ 612-2 



10 



+ 875-5 



18 



- 583-5 



23 



- 850-5 



730-4 



731-5 



8-33067 



•0000099 



1-8 



6 



+ 907-5 



9 



+ 1238-2 



19 



- 8900 



22 



-1227-0 



1065-7 



1067-4 



8-49577 



-0000099 



1.7 



7 



+ 1184-5 



8 



+ 1500-5 



20 



-1125-0 



21 



-1505-5 



1328-9 



1331-0 



8-58925 



-0000096 



Away 



6 



- 66-5 



11 



+ 28-5 



1 



- 44-5 















2-6 



7 



+ 190-2 



10 



+ 338-0 



2 



- 280-7 



5 



- 349-5 



289-6 



290- 1 



7-94533 



0-0000101 



1-8 



8 



+ 899-0 



9 



+ 1172-0 



3 



- 912-5 



4 



-1188-0 



! 



1045-4 



1047-5 



8-49577 



-0000103 



