226 



Royal Institution. 



ficulty of observing facts having any relation to time, and because 

 two gravitating particles or masses did not seem to have any neces- 

 sary dependence on each other, for the existence or excitement of 

 their mutual power*. On the present occasion a passage was quoted 

 from Newton which had since been discovered in his works, and 

 which, showing that he was an unhesitating believer in physical 

 lines of gravitating force, must from its nature rank him amongst 

 those who sustain the physical nature of the lines of magnetic and 

 electrical force; it is as follows, in words written to Bentley f : 

 " That gravity should be innate, inherent and essential to matter, so 

 that one body may act upon another at a distance through a vacuum, 

 without the mediation of anything else, by and through which their 

 action and force may be conveyed from one to another, is to me so 

 great an absurdity, that I believe no man who has in philosophical 

 matters a competent faculty of thinking, can ever fall into it. Gra- 

 vity must be caused by an agent acting constantly according to cer- 

 tain laws ; but whether this agent be material or immaterial, I have 

 left to the consideration of my readers." 



Finally, reference was made to Sabine's remarkable observation, 

 sustained as it has been by Wolf, Gautier and others, of certain 

 coincidences existing between the appearance of solar spots and the 

 diurnal variation of the magnetism of the earth. Schwabe has 

 been engaged in carefully observing the spots on the sun since the 

 year 1826. He has found them gradually to increase in number and 

 size from year to year, and then decrease ; then again increase, again 

 to decrease, and so on in a regular period of about ten years. The 

 following is a part of his table X giving the years of the maxima and 

 minima of spots : — 



Lamont (Dec. 1851)§ was induced by recent researches in atmo- 

 spheric magnetism, to examine the daily magnetic variation in 

 declination, and found that, as a whole, it increased and diminished, 

 and then increased again, having a regular variation of about ten 

 years: the year 1844 was given as ha\'ing a minimum variation of 



* PhU. Mag. S. 4. 1852, vol. iii. p. 403 (3246). 



t Newton's Works, Horsley's edition, 4to, 1783, vol. iv. p. 438, or the 

 Third Letter to Bentley. 



X Humboldt's Cosmos, iii. p. 291, 292. Bibliothkque Universelle, 1852, 

 XX. p. 184. 



§ PoggendorflTs Annalen, Ixxxiv. p. 672. [Phil. Mag. June, 1852.] 



