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showed that if a magnet be broken each piece becomes a complete 
magnet. The opinions of Rittenhouse, however, seem to be 
greatly more clear and precise. The idea of ‘‘ magnetical 
particles ’’ each having a north anda south pole, and each retaining 
its polarity, even when the metal is fused, is a perfectly definite one. 
When a piece of iron shows no magnetism, it is because the 
particles lie irregularly, and mutually neutralize one another’s 
action; the process of ‘magnetization consisting simply in 
arranging these particles so that their similar pcles face similarly. 
If now we take into the account the fact that the paper of Ritten- 
house antedates that of Kirwan by about sixteen years, it would 
seem clear that to our fellow-member belongs indisputably the 
credit of the origin of the molecular theory of magnetism. 
Alexander Dallas Bache was elected a member of the American 
Philosophical Society, April 17, 1829; only a few months after he 
had taken up his residence in Philadelphia as Professor of Natural 
Philosophy and Chemistry in the University of Pennsylvania. His 
attention was early directed to the subject of Terrestrial Magnetism 
by the remarkable investigations in this direction made by Gauss 
and Weber. And, in 1830, he erected and equipped a little mag- 
netic observatory in the garden attached to his residence, in which 
observations were made regularly for a period of four or five years. 
It was in this observatory that, aided by his wife and by his pupil, 
John F. Frazer, he determined with accuracy, for the first time in 
this country, the periods of the daily variations of the magnetic 
needle. Here, also, by another series of observations, he deter- 
mined the connection of the fitful variations of the direction of the 
magnetic force with the appearance of the aurora borealis. His 
first memoir on the subject was presented to the American Philo- 
sophical Society in November, 1832, and contains the results of 
hourly observations on the declination.* These observations were 
made with a very long needle provided with a graduated arc at each 
end. ‘Terrestrial magnetism soon became with him a favorite sub- 
ject and one to which he continued to make valuable contributions 
at intervals during his whole life. Even in his journeys he carried 
with him portable instruments with which he ‘determined the mag- 
netic constants of the points he visited. ‘‘ What he accomplished 
in later years for this favorite branch of science,’’ says Dr. Gould, 
**“On the Diurnal Variation of the Magnetic Needle,” Trans. Amer. Philos. Soc. (New 
Series), Vol. v, p. 1. 
