MAGNETIC OBSERVATIONS AT AND NEAR 

 ALBANY, N. Y., BETWEEN THE YEARS 1686 

 AND 1892. 



[Read before the Albany Institute, January 4, 1888; Revised to December 1, 1892.] 



Physical science affords no more interesting phenomenon than ter- 

 restrial magnetism. An invisible, yet potent omnipresent force, it is 

 as important in its functions as is gravitation; and may, indeed, be a 

 form or mode of energy supplementary to that greater power by which 

 rivers run their courses downward to the sea. Terrestrial magnetism, 

 however, differs from gravitation in being, even locally, an inconstant 

 force; varying in accordance with its own local laws, and controlled by 

 causes as yet little understood; yet penetrating and traversing even the 

 massive mountains which gravitation holds so rigidly in place. 



Every one appreciates the all-pervading nature of gravitation. 

 Under its control the snow flakes fall steadily and regularly toward the 

 earth. In obedience to gravitation the torrent of Niagara pours con- 

 tinuously into its gulf ; and, at the command of this invisible force the 

 Moon pursues the "World ; while the most distant planets, in their 

 courses, majestically keep the orbits which the laws of gravitation pre- 

 scribe. 



When, after studying the wonderful symmetry and system of this 

 great force, we encounter another mode of energy in matter, with an 

 influence extending not only throughout the World but also — in all 

 probability — throughout the Universe; associated with the phenom- 

 ena of light, heat and electricity; we cannot but believe that this, the 

 so-called terrestrial magnetism, is a condition of energy in matter that 

 might be called, with better reason, Cosmical Magnetism; the natural 

 magnetism of matter in space; and as much a portion of the celestial 

 mechanism as gravitation itself. 



It is true that the force controlling magnetism is, like electricity, 

 invisible. When we speak of magnetism we refer to the reaction of 

 this invisible force upon visible magnetic bodies; the substances* we 



