Abstracts foe the Magnetic Dip. 



155 



TABLE XXVII. — Monthly Mean Values of A fi, the Differences of Magnetic Dip, for the Observation Hours of 

 1842, deduced from Tables X. and XVIII. ; the value of A ^ December 2'^ being taken as Zero. 



Month. 



aoh. 



SSI". 



2h. 



5i>. 



Mean of the 

 Pour Hours. 



Range. 



Mean of 

 201^ and 5K 



Difference of 

 20^ and 5^. 



January 



6-11 



6-62 



5-56 



5-71 



600 



l'06 



5-91 



6-40 



February 



604 



6-51 



5-63 



5-16 



5-83 



1-35 



5-60 



0-88 



March 



518 



5-99 



4-51 



401 



4-92 



1-98 



4-59 



M7 



April 



5-59 



617 



4-61 



3-56 



4-98 



2-61 



4-57 



203 



May 



4-62 



512 



3-39 



3-26 



410 



1-86 



3-94 



1-36 



June 



4-34 



4-84 



2-95 



2.06 



3-55 



2-78 



3-20 



2-28 



July 



4-22 



4-42 



2-40 



205 



3-27 



2-37 



313 



217 



August 



3-83 



4-45 



2-28 



1-73 



307 



2-72 



2-78 



2-10 



September 



2-88 



3-83 



221 



1.99 



2-73 



1-84 



2-43 



0-89 



October 



1-64 



2-47 



1-38 



1-44 



1-73 



103 



1-54 



0-20 



November 



115 



1-60 



0-97 



0-95 



M7 



0-65 



1-05 



0-20 



December 



0-23 



0-60 



000 



007 



0-22 



0-60 



0-15 



0-16 



A ^ =: -J- sin 2 d 



The Table above was computed from the formula 

 I aY aX -) 



A Y . aX 



—y^ was obtained from Table X., and y from Table XVIII. ; 6 being taken at 71° 18'. 



The followincr Table has been formed from the above. 



TABLE XXVIII. — Mean Values of A ^ for Three Months, for the Summer and "Winter Months, and for the 



Year 1842. 



Period. 



20\ 



23''. 



2'^. 



5h. 



Mean of the 



Range. 



Mean of 



Difference of 













Pour Hours. 



20»' and 5^. 



20'" and 5'". 



1842. 



















Jan., Feb., March 



5-78 



6.37 



5-23 



4-96 



5-58 



1-41 



5-37 



0-82 



April, May, June 



4-85 



5-38 



3-65 



2-96 



4-21 



2-42 



3-90 



1-89 



July, Aug., Sept. 



3-64 



4-23 



2-30 



1-92 



3-02 



2-31 



2-78 



1-72 



Oct., Nov., Dec. 



1-01 



1-56 



0-78 



0-82 



1-04 



0-78 



0-91 



0-19 



Jan., Feb., March, \ 

 Oct., Nov., Dec. J 



3-39 



3-96 



300 



2-89 



3-31 



107 



3-14 



0-50 



April, May, June, ) 

 July, Aug., Sept. J 



4-24 



4-80 



2-97 



2-44 



3-61 



2-36 



3-34 



1-80 



The Year 



3-82 



4-38 



2-99 



2-66 



3-46 



1-72 



3-24 



116 



The columns containing the means and differences of 20'' and 5^ have been given for comparison with the 

 Magnetic Dip, obtained from the Inclinometer at these hours. 



The winter months indicate a maximum Dip about 23'*, and a minimum between 2^ and 5'S apparently 

 nearer 6^ than 2** in the first quarter of 1842, but nearer 2'* than 5^ in the last quarter. The maximum seems 

 to occur somewhat earlier, and the minimum later, in the summer than in the winter months. 



The ratio of the difference of Dip at 20'* and 5'* in winter to that in summer is nearly the same from both 

 Tables XXVI. and XXVIII., though the quantities arerather different. 



The annual diminution of Dip from Table XXVII. appears greater than that from the observation of the 

 Inclinometer. 



