330 Mr. P. E. Chase on Gravity and Magnetic Inclination. 



renewed reasons for regretting the want of a complete record 

 of the investigations on which Professor Secchi based his con- 

 clusion, that all " the phenomena hitherto known of the diurnal 

 magnetic variations may be explained by supposing that the sun 

 acts upon the earth as a very powerful magnet at a great dis- 

 tance"*. As I know of no magnetic law which will account for 

 those anomalies, I propose briefly to describe them, and to point 

 out some relations between the gravitation-currents and the dip 

 of the needle, as a sequel to my papers on the influence of gra- 

 vity upon the total magnetic force and the magnetic declination. 

 General Sabine's discussions have shown some important points 

 of difference between the magnetic disturbances at intertropical 

 and extratropical stations, the Cape of Good Hope being mag- 

 netically, though not geographically, intertropical. In the third 

 volume of the ' Toronto Observations/ and in Professor Bache's 

 discussions of the observations at Girard College, projections of 

 the daily and semiannual inclination-curves are given f; and 

 plate 5 of the second volume of the ' Hobarton Observations * 

 contains a graphical representation of the diurnal variations of 

 the inclination at the different observation-hours in the four 

 seasons. If we also project, from General Sabine's Tables of the 

 mean results, the daily and semiannual curves at St. Helena 

 and Cape Colony, and compare the curves at the five stations, it 

 will be found that, 



1. The greatest daily disturbance of inclination occurs about 

 noon. 



2. At (magnetically) intertropical stations the dip is dimi- 

 nished, but at extratropical stations it is increased in the middle 

 of the day. 



* Phil. Mag. S. 4. vol. ix. p. 452. Faraday (Experimental Researches, 

 vol. iii. p. 493) states " that the celebrated Professor Gazzaniga, starting 

 from his numerous experiments, which demonstrate the influence of mag- 

 netism upon the same aerial fluids in a manner therefore different from 

 that of Bancalari, was induced to consider the sun and all the other celes- 

 tial bodies as so many enormous magnets ; by which he established that at- 

 traction is merely one effect of the magnetism of the great celestial masses 

 placed at an enormous distance — an idea which reappeared in 1346 in 

 Prussia, and in 1847 in France." 



While admitting the intimate relationship of magnetism and gravity, I 

 must dissent from the learned Professor's inference. For the evidence ap- 

 pears irresistible, that the earth's magnetism is directly dependent on the 

 terrestrial gravitation of the thermally disturbed aerial currents, and that it 

 is only slightly aifected by the perturbations of solar and lunar gravitation ; 

 so that if we regard the relationship as a causal one, magnetism rather than 

 attraction should be considered the effect. (See Gauss, " General Theory 

 of Terrestrial Magnetism," §§30, 40, Taylor's Scientific Memoirs, vol. ii. 

 p. 232.) 



t By the kindness of Professor Henry I have been permitted to refer to 

 the proof-sheets of the Fourth Section of Professor Bache's 'Discussions.' 



