120 



ON THE NUMERICAL RELATIONS OF GRAVITY AND MAGNETISM. 



II. 



TABLE II. SOLAR-DIURNAL VARIATION IN THE MAGNETIC FORCE AT ST. HELENA, IN HUNDRED-THOUSANDTHS 



OF THE TOTAL FORCE. 



Time. 



Oh. 



1 h. 



2h. 



8 h. 



4h. 



8 h. 



6 h. 



7h. 



8h. 



<> I.. 



10 h. 



11 h. 



A.M. 



P. M. 



—43 



+ 95 



—41 



+ 82 



—38 

 + 00 



—30 

 +40 



—35 

 + 20 



—34 



+ 1 



—32 

 —15 



—20 



—20 



+ 3 

 —36 



+ 34 

 —41 



+68 



—45 



+85 

 —45 



A simple inspection of the above table will furnish evidence of the truth of Prop. II. 

 The relation of the magnetic to the tidal variations between 6 A. M. and 6 P. M. is more 

 clearly shown by 



TABLE III. HOURLY MAGNETIC DIFFERENCES DURING THE DAY HOURS. 



1st h. 2d h. .'id h. 



Before 9 A.M., 31 23 12 



After 9 a.m., 29 22 10 



IJcfore 3 i>. m., 20 22 13 



After 3 p. m., 20 I!) 16 



100 86 51 



Tidal ratios, 100 73 27 



Ratios of squares of mean magnetic 



differences, 100 74 26 



For further illustrations, see the discussion of Prop. V. 



III. 



If we examine the position of the aerial rotation-spheroid, it will be seen that when the 

 moon is approaching syzygy, at a distance of about 30°, in addition to the normal tidal 

 action due to her situation relatively to the sun, she exerts a compressing force which tends 

 to raise the daily average of the barometer, while, at the same distance before her quadra- 

 ture, this secondary influence serves to increase the ellipticity and depress the barometric 

 daily average. At intermediate points a portion of her attraction is employed in turning 

 the aerial spheroid, thus producing a condensation of the air and elevation of the barometer, 

 or a rarefaction and barometric depression, according as the spheroid is turned against the 

 direction of the earth's rotation, or the contrary. Hence there result, besides the primary 

 low barometer at syzygies, and high at quadratures, secondary low at 60° and 240°, secon- 

 dary high at 150° and 330°, and tertiary high and low at some less definitely marked 

 intermediate points. (Op. citat., p. 398.) I designate the tides as primary, secondary, and 

 tertiary, not in the order of relative magnitude, but of stability and simplicity. The 





