1868.] 



369 



[Chase. 



difliciilt to assign to such eft'ects any other than a cosmical 

 cause. The greater proximity of the earth to the sun in the 

 December compared with the June solstice most naturally pre- 

 sents itself as a not improbable cause ; but we are as yet too 

 little acquainted with the mode of the sun's action on the mag- 

 netism of the earth to enter more deeply into the question at 

 present." 



That the coincidence which is here suggested with th(! com- 

 mendable caution and modesty of a truly philosophic spirit, is 

 the indication of a vera causa, seems to me indubitable. In 

 Mr. Broun's recent!}^ published discussions of the " diurnal 

 variation of the magnetic declination at Trevandrum, near the 

 magnetic equator, and in both hemispheres " (Trans. R. S. of 

 Edinburgh, vol. 24), data are collated for some more than 

 usuall}' satisfactory general averages of magnetic variations, 

 which are interesting, both on account of their incidental con- 

 firmation of Sabine's hypothesis, and on account of the confi- 

 dence which ma}^ be reasonably attached to all evident deduc- 

 tions from properly authenticated mean values. Ten stations 

 are chosen for comparison, five of which are in north, and five 

 in south (magnetic) latitude, the mean latitude coinciding 

 nearl}' with the magnetic equator, as is shown by the following 

 table. 



VOL. X. — 2z 



