Lovering and Bond on Magnetic Observations at Cambridge. 29 
vations appears, on the whole, unfavorable for drawing conclusions 
in regard to the concurrence of abrupt changes of the magnetic 
state of the earth as it is the period when the bar is most quiet. 
It is of advantage, however, to know that the periods of repose are 
independent of longitude and the same absolutely for different 
places; an inference which the observations certainly authorize us 
to make. We shall have occasion hereafter to remark on the de- 
gree to which observations made with the Gauss Magnetometer and 
Lloyd’s Declination instrument are comparable. 
Whatever interpretation may be given to the anomalous changes 
to which the declination of the magnetic meridian is subject, there 
can be little hesitation in admitting that the regular and _periodi- 
cal ones having their expression in functions of solar time are de- 
pendent upon the sun’s influence as an exciting and sustaining 
cause. The theory which we may adopt as to the nature of the 
earth’s magnetism does not essentially affect this statement. If 
magnetism, as an independent property, exist in particles of the 
earth’s mass, it may have its equilibrium disturbed by temperature 
as heat is known to affect the state of ordinary steel magnets ; and 
as in the passage of the sun through his daily and yearly path parts 
of the earth’s surface are heated to unequal degrees, that change of 
the magnetic fluid may be induced which shall result in periodical 
alterations of the magnetic meridian. But a strong body of evi- 
dence can now be summoned to prove that magnetism has no 
existence as an independent fluid or property of matter; but that 
vals by himself and Professor Bache on the small variations of magnetic de- 
clination. The result of the comparison has convinced him that such changes 
do not occur simultaneously at places so far removed from each other as Dub- 
lin and Philadelphia. Therefore they will not, as was suggested, furnish a 
safe method of deducing differences of longitude. 
