82 Mr. J. A. Broun on Terrestrial Magnetism. 



for the winter groups and summer groups of lunations for the 

 magnetic inclination and total force were given at each lunar 

 hour in the same volume. The results for the lunations of both 

 years for the two components of force were projected and will be 

 found in the Edinburgh Transactions, read in January and April 

 1846. General Sabine's investigation, which I have not yet 

 seen, dates, I believe, in 1856. 



Besides the results for these elements, I have given in the 

 general results (published in 1 850) the projections of the diurnal 

 curve, due to lunar influence, described by the north end of a 

 needle freely suspended in the direction of the magnetic dip. 

 As I have not noted in the volume referred to the results dedu- 

 cible from this curve, I shall state them shortly here. 



1st. The amount of motion due to lunar influence of a freely 

 suspended needle is a maximum twice in a lunar day, namely 

 during the hours before and after the moon's transit of the infe- 

 rior meridian, and at the transit of the superior meridian. It 

 is a minimum twice ; a principal minimum six hours after the 

 superior transit, and a secondary minimum six hours after the 

 inferior transit. 



2nd. The gi-eatest amount of motion occurs while the moon 

 is below the horizon. This result, if confirmed, is very curious, 

 as it is wholly opposed to all that we know of the solar action. 



3rd. The direction of motion is, on the whole, the opposite to 

 that produced by the solar influence, from one hour after the 

 moon's passage of the superior meridian to one hour after the 

 passage of the inferior meridian ; and it is the same as that due 

 to the sun in the remaining twelve hours. 



The following are the approximate angular movements of the 

 needle due to the moon's action for different intervals, deduced 

 from observations at Makerstoun during twenty-five lunations, 

 1844, 1845. 



Moon's inferior transit 



Moon's superior transit 



I shall now refer to the laws of magnetic disturbance. 

 Diurnal laic, — The fact that the movements of the declination- 



