INVESTIGATION 



INFLUENCE OF THE MOON ON THE MAGNETIC DECLINATION. 



THE existence of a sensible lunar effect on the magnetic decimation has already 

 been established by the labors of Broun, Kreil, Sabine, and others. It is never- 

 theless important to add the weight of new numerical results to those already 

 obtained. 



In the discussions of the Philadelphia observations of magnetic declination, 

 already presented to the Association, I have shown how the influence of magnetic 

 disturbances, of the eleven year period of the solar diurnal variation and its annual 

 inequality, of the secular change, and of the annual variation may be severally 

 eliminated, leaving residuals from which the lunar influence is to be studied. Each 

 observation was marked with its corresponding lunar hour and the hourly normals 

 used for comparison. 



This method of treatment of the subject is that followed by General Sabine in 

 his discussion of the results of the British observations. 1 



The details of the method will be better understood by an example. 



The time of the moon's passage over the meridian of Philadelphia (upper transit) 

 was obtained from the American Almanac, the small correction for the difference 



1 In reference to methods and results, in general, on this subject, the following papers may be consulted : 

 Observations in Magnetism and Meteorology made at Makerstown, in Scotland, in the observatory of 

 General Sir Thomas M. Brisbane, Bart., in 1845 and 1846, forming vol. xix., parti, of the Trans. Royal 

 Society of Edinburgh. By John Allan Broun. Edinburgh, 1849; also vol. xix. part ii., containing 

 the general results (1850). 



Einfluss des Mondes auf die magnetische Declination by Carl Kreil. Vol. iii. of the Proceedings of 

 the Mathematical and Physical Section of the Imperial Academy of Sciences of Vienna, 1852; also, 

 vol. v., ibid., 1853. 



Philosophical Trans. Royal Society, art. xix., 1853: On the Influence of the Moon on the Magnetic 

 Declination at Toronto, St. Helena, and Hobarton. By Col. E. Sabine. 



Phil. Trans. Royal Society, art. xxii., 1856: On the Lunar-diurnal Magnetic Variation at Toronto. 

 By Major General E. Sabine. And 



Phil. Trans. Royal Society, art. i., 1857 : On the evidence of the Existence of the Decennial Inequality 

 in the Solar-diurnal Magnetic Variations and its Non-existence in the Lunar-diurnal Variation, of the 

 Declination at Hobarton. By Major General E. Sabine. 

 1 



