Lovering on Magnetic Observations at Cambridge. 147 
instrument is used for differential quantities, may stand out in 
their full magnitude in the other application of it. It appears, 
therefore, that the Inclination and the Vertical Component, which 
are functions of each other and of the Horizontal Force, are 
not yet susceptible of the same accurate determination which is 
claimed for the other elements of Terrestrial Magnetism. All the 
methods that have been used for observing inclination require so 
much time as to preclude the idea of observing directly moment- 
ary changes of inclination, and deducing from them corresponding 
variations in the Vertical Force. The Dipping Needle of Mr. 
Fox, a full description of which may be found in several sci- 
entific journals, furnishes a more convenient and exact method of 
determining dip and intensity than the ordinary Dipping Needle. 
An observation was made on the dip at Cambridge with one of 
these improved instruments, by Lieutenant Lefroy, of the Toronto 
Magnetic Observatory, which gave the mean dip at that place on 
October 3d, 1842, between 10h. 30m. and 11h. 30m., mean solar 
time at Cambridge, 74° 19.5. An instrument of this kind is now 
placed at the Cambridge Observatory, from which more accurate 
observations on dip may be expected than have yet been made 
at this place. 
The observations at Cambridge have been published chiefly 
with a view to their easy distribution, and not with the expecta- 
tion of deducing from them alone any of the great laws of mag- 
netic influence on our planet. However long and complete such 
a series of observations might have been considered formerly, it 
forms but a small part of the rich fund that has been or will 
be created by the recent codperation of so many observers in 
remote parts of the earth, in Observatories stationed and appointed 
for this purpose, with all the wisdom and munificence which 
