Lovering and Bond on*Magnelic Observations at Cambridge. 27 
ment is confined chiefly to the extent or the existence of the motion. 
At 121, 74, 94 o’clock Gott. M. T. some excursions appear in the 
Philadelphia curve which have little or no counterpart in the Cam- 
bridge curve. They are deserving of notice because they are more 
considerable than any others of a local character which have been 
noticed and yet they do not, any of them, exceed 5’ of are. But the 
remarkable excursions in Plate II. at a, b, c, d, e, f, are all faithfully 
represented on the Philadelphia curve. Only the upper branches 
which belong to the easterly motion are exceeded by the correspond- 
ing simultaneous movement at Philadelphia, while the grand excur- 
sions at the bottom of the Plate, which are due to the westerly motion 
or increase of declination, go beyond their parallel passages in the 
Philadelphia curve. For instance, the branches 8, ¢, d, e, f, extend 
respectively 10’, 12’, 11', 5‘, 6’, farther in the Philadelphia than the 
Cambridge curve. The reverse happens at g, h, 7, where the Cam- 
bridge branches go 13’, 30’, 142’, farther west than the analogous 
ones at Philadelphia. The close coincidence of the times when the 
direction of any great motion changes, observed at Toronto, Phila- 
delphia and Cambridge, makes it probable that the longitudes of the 
three places are known to a close approximation, or, at least, that 
the differences of longitude between these places are not much in 
fault; for, if they were, it would by its effect upon the regulation of 
the clocks prevent a coincidence of magnetic disturbances which 
actually existed and make the appearances different from what we 
observe; unless we can suppose what seems extremely improbable, 
that the constant error of the time should by chance balance pre- 
cisely the actual want of coincidence in the arrival of the magnetic 
impulse at each place so as to deceive us in the final result. This, 
however, is a subject which requires to be pursued longer. The 
observations contemplated in coming years will, it is believed, fur- 
