756 



J. A. BROUN ON THE LUNAR DIURNAL VARIATION OF 



for April and May. In the former month, the needle moves westwards, in the 

 latter eastwards from the hour when the moon is on the inferior meridian 

 (sunrise). 



TABLE II. — Mean Lunar Diurnal Variation on seven successive days, for the Moon on the Meri- 

 dians of 18 h. to 12 h. at 6J A.M., in January and December, derived from seventeen 

 quarter Lunations, 1856-65.* 



1 Solar Hour, 

 M. T. 



Id. 



2d. 



3d. 



4d. 



5d- 



6d. 



7d. 



12| A.M. 



- 0-05 



- 0-13 



+ 0-07 



+ 0-06 



- 0-16 



- 0-11 



- 0-05 



i l 



x 2 » 



- 0-06 



- 0-10 



+ 0-13 



+ 0-03 



- 0-16 



- 0-09 



- 0-03 



9 1 



- 0-07 



- 0-07 



+ 0-07 



+ 0-03 



- 0-07 



- 0-00 



+ 0-02 



°2 » 



- 0-10 



- 0-14 



+ 0-16 



+ 0-04 



+ 0-01 



+ 0-09 



- 0-05 



4A 



- 0-13 



- 0-14 



+ 0-08 



+ 0-06 



+ 0-05 



+ o-io 



+ 0-16 



H ,, 



- 0-35 



- 0-20 



- 0-06 



+ 0-04 



+ 0-14 



+ 0-20 



+ 0-24 



H » 



- 0-69 



- 0-55 



- 0-24 



+ 0-06 



+ 0-40 



+ 0-48 



+ 0-54 



n n 



- 0-62 



- 0-51 



- 0-57 



- 0-29 



+ 0-22 



+ 0-37 



+ 0-62 



H „ 



- 0-32 



- 0-38 



- 0-82 



- 0-25 



- o-io 



+ 0-16 



+ 0-39 



H „ 



+ 0-15 



+ 0'08 



- 0-72 



- 0-18 



- 0-48 



- 0-35 



- 0-06 



10i „ 



+ 0-48 



+ 0-11 



- 0-40 



+ 0-13 



- 0-91 



- 0-58 



- 0-64 



Hi » 



+ 0-43 



+ 0-23 



— 0-17 



+ 0'26 



- 0-66 



- 0-52 



- 0-79 



OJ P.M. 



+ 0-31 



+ 0-40 



-I- 0-08 



+ 0-25 



- 0-31 



- 0-36 



- 0-61 



11 

 x 2 >' 



+ 0-11 



+ 0-34 



+ 0-46 



+ 0-09 



- 0-44 



- 0-08 



- 0-55 



91 



- 0-20 



+ 0-18 



+ 0-45 



+ o-ii 



- 0-38 



+ 0-36 



- 0-35 



H ,, 



- 0-37 



- 0-23 



+ 0-29 



+ 0-12 



+ 0-22 



+ 0-58 



+ 0-07 



41 



- 0-43 



- 0-44 



- 0-04 



+ 0*12 



+ 0-47 



+ 0-51 



+ 0-47 



°2 )j 



- 0-38 



- 0-62 



— 0-14 



- 0-09 



+ 0-26 



+ 0-24 



-|- 0-25 



6J „ 



- 0-19 



- 0-15 



- o-io 



- 0-12 



+ 0-05 



+ 0-12 



+ o-io 



H „ 



- 0-17 



- 0-20 



- 0-11 



- 0-12 



- 0-02 



+ O04 



+ 0-16 



8i „ 



- 0-20 



- 0-11 



- 0-08 



- o-ii 



- 0-04 



+ 0-05 



+ 0-04 



9* „ 



- 0-12 



- 0-07 



- 0-07 



- o-io 



- 0-16 



+ 003 



+ 0-02 



10J „ 



- 0-09 



- 0-05 



- 0-13 



- 0-09 



- 0-03 



+ 0-02 



- 0-05 



H'i ,. 



- O'll 



- 0-09 



- 0-09 



- 0-15 



- 0-05 



- 0-07 



- 0-12 



12* „ 



- 0-11 



- 0-06 



- 0-04 



- 0-18 



- 0-12 



- 0-10 



- 0-15 



Mean hour \ 

 angle of 1 

 the moon r 

 at 6Ja.m. ) 



h. 

 18-06 



h. 

 17-04 



h. 

 16-07 



h. 

 15-05 



h. 

 14-05 



h. 

 13-10 



h. 

 1205 



58. If we now examine the epochs near sunset, we find that on the first day 

 the needle has turned (though little) an hour before the sunset observation; on 

 the second clay it turns at the sunset observation; on the third day the move- 

 ment is arrested, or nearly so, from sunset to sunrise; on the fourth day the 

 movement westwards ceases at sunset; on the fifth clay it has begun to move 

 eastwards an hour before; on the sixth, two hours before; and on the seventh, 

 one hour before the observation nearest sunset. I think there is little doubt 

 that there is a relation betwixt the direction of movement and sunset like that 



* The means for 1 2J a.m., are calculated for the end of each day as well as for the beginning, in 

 order to connect in the projection the value for the end of each day with that for the beginning of the 

 next. 



