ixxiv 



Genekal Results of the Makeestoun Observations. 



these i-emarks may be kept in view, in considering the numbers in the following Table, which are obtained from 

 Plate VIII. 



Table 68. — Angular Distances between the Disturbed and Undisturbed Positions for each Hour in the 

 motion of a freely-suspended Dipping-Needle, as obtained from Plate VIII. 



[ 

















Year. 



Mak. E 



ec. ,, 







T 1 Sept. 



Sept. 



March 







Mean J 



Ma 



rch. May. 1 



J"ly- Oct. 



to 



to 



Prom 



Mean 



Time. P 



eb. A 



pril. Ji 



ine. 



^"S- Nov. 



Feb. 



Aug. 



Mean 



of first 5 



















Curve. 



Columns. 



h. 



12 0- 



36 0- 



20 0- 



34 



0-28 0- 



36 



0-35 



0-25 



0-32 



0^32 



13 



26 



32 



26 



•24 



28 



•28 



•31 



•26 



■27 



14 



28 



46 



20 



•18 



14 



•18 



•28 



•24 



•24 



15 



09 



16 



16 



•06 



12 



•08 



•12 



•08 



•12 



16 



06 



04 



18 



•08 



12 



•09 



•09 



•04 



•09 



17 



15 



08 



08 



•24 



14 



•13 



■14 



•08 



•14 



18 



21 



20 



08 



•32 



34 



•25 



•18 



•22 



•24 



19 



20 



24 



14 



•32 



40 



•29 



•22 



•26 



•27 



20 



18 



30 



30 



•46 



42 



•29 



■34 



•28 



•33 



21 



22 



36 



28 



•30 



40 



-30 



■32 



•32 



•31 



22 



24 



28 



26 



•20 



26 



•28 



• 22 



•28 



•25 



23 



24 



30 



16 



•36 



26 



•24 



•18 



•24 



■26 







28 



28 



12 



•14 



30 



•26 



•18 



•22 



■23 



1 



35 



24 j 



•28 



•16 



24 



•28 



•24 



•28 



•26 



2 



•36 



36 



•40 



•16 



38 



•34 



•30 



•34 



•34 



3 



•29 



•32 



■26 



•24 



•36 



•30 



•28 



•28 



•30 



4 



•28 



•44 



•46 



•44 



•16 



•40 



•44 



•32 



•33 



5 



•12 



•30 



•34 



•50 



•12 



•04 



•35 



• 18 



•26 



6 



•15 



•36 



•30 



•42 



■32 



•19 



• 28 



•16 



•30 



7 



•18 



•42 



•30 



•26 



•38 



•27 



•22 



■24 



•30 



8 ! 



•43 



•36 1 



•16 



•24 



•58 



•50 



•24 



• 38 



•38 



9 



•38 



•38 



•24 



•44 



•44 



•38 



•34 



•38 



•38 



10 



•39 



•38 



•30 



•36 



•52 



•45 



•34 



•40 



•40 



11 



1 



•42 



•26 



•38 



•22 



•50 



•45 



•32 



■38 



•37 



166. The following are the conclusions from Table 68 : — 



\st. In the two figures for the months from September to February, the effect of disturbance in displacing 

 the needle is a minimum about 4'' a.m. and 4"^ p.m., the values for these hours being nearly equal, or near the 

 hours when the sun is on the magnetic prime vertical. The maximum effect of disturbance occurs in both about 

 10*^ P.M., when the sun is on the magnetic meridian, a secondary maximum occurring in the figure December to 

 February about 1^^ p.m., and in the figure September to November about 8'* a.m. 



2d, In the figixre for March-April, the minimum occurs about 4'^ a.m., and the maximum probably about 

 S^-IO'' P.M., the value, however, varying little for the 18 hours from 8^^ a.m. till 2'^ a.m. 



3c?, The mean of the two resixlts for the figures May-June and July-August is to some extent the reverse 

 of the result for December to Februaiy. The effect of disturbance is a minimum about 4'' a.m., and about 

 noon ; it is a maximum about 8** a.m. and 4** p.m. It would appear, therefore, that the diurnal law of the 

 effect of disturbance varies with season as well as the law of the amount of disturbance (see Nos. 45, 77, 110) : 

 a minimum is also shewn about 8^ p.m. 



4:th, In all months of the year the effect of disturbance is a minimum about 4'' a.m. In the winter months 

 a minimum occurs at 4^^ p.m., the maximum occurs at the same hour in the summer months. 



5th, In the mean figure for the year, minima occur at 4'' a.m. and about 5§^p.m., the maximum occurs about 

 10'' p.m., and a maximum occm-s between 8"^ a.m. and 4^ p.m. If, making allowance for the effect of dis- 

 tui'bance on the position of the centre of gTavity with reference to dip (No. 121), we suppose the centre of 

 gravity of the dotted figure for the year (Plate VIII.) raised 0'-15 on the line of mean declination, or that of 

 the continuous figures lowered as much, we find the maximum effect of disturbance to occur about 10** p.m. 

 and lO** a.m., and the minimum effect about 4** a.m. and 5^ p.m. This result was obtained for the magnetic de- 

 clination in 1844. See the Volume for that year, p. 346, 



L 



