Chase.] gg [April. 



single force." In my various subsequent papers, and especially in 

 the one to which the Magellanic Premium was awarded, [Op. citat, 

 and Trans. A. P. S., Vol. XIII, N. S. Art. VI,] I pointed out va- 

 rious reasons for supposing that the primal unitary force is the same 

 that controls the motions of the several stellar systems, — in other 

 words, the force of gravitation, — or perhaps of simple undulation, — 

 which is manifested as heat in one of its subordinate forms, and as 

 attraction in another. The numerical relations which I demon- 

 strated between the disturbances of weight and of total magnetic 

 force, were certainly noteworthy, and to my own mind, extremely 

 satisfactory; and as further investigations have afforded additional 

 confirmation of my views, I desire to put upon record a brief notice 

 of the general harmony which mutually characterizes the gravitation 

 currents and the variations of magnetic declination. 



Preliminary investigations showed, as might have been reasonably 

 anticipated, that the best quantitative results can be obtained from 

 the observations at stations near the equator, and I therefore based 

 my reasoning, in great measure, upon the St Helena records, and 

 Maj. Gen. Sabine's discussions, confirming it by such incidental re- 

 ferences to other observations, as seemed available for the purpose. 

 At the same time allusion was made [Trans. A. P. S., loc. citat., 

 p. 132], to researches now in progress, which may probably enable 

 us to discover numerical relations, that will be equally satisfactory, 

 from an examination of the observations in higher latitudes. While 

 patiently and confidently awaiting the completion of those researches, 

 it may be well to present some considerations which will serve both 

 as a corroboration of my own views, and as a guide to the investiga- 

 tions of others. 



The discussions of the magnetic and meteorological observations 

 at Girard College [Coast Survey Reports, and Smithsonian Contribu- 

 tions], should be specially interesting to all Americans, and they are 

 also among the most recent and valuable publications on terrestrial 

 physics. From them I quote the following references to the most 

 important and best established normal disturbances of declination. 



I. " The annual variation depends on the earth's position in its 

 orbit; the diurnal variation being subject to an inequality depending 

 on the sun's declination. The diurnal range is greater when the 

 sun has north declination, and smaller when south declination; the 

 phenomenon passing from one state to the other about the time of 

 the equinoxes." [Part II, p. 10. See, also, Toronto Obs. 2, xvii, 

 St. Helena Obs., 2, cxviii.] 



