m 
S deniific, IntelUgcnce. 
being in the same line), and laying the magnets so joined flat 
upon the needle with their poles upon its centre ; then having 
elevated the distant extremities of the magnets, so that they may 
form an angle of about two or three degrees with the needle^ 
they are to be drav/n from the centre of the needle to the extre- 
mities, carefully preserving the same inclination, and having 
joined the poles of the magnets at a distance from the needle, 
the operation is to be repeated ten or twelve times on each sur- 
face. — 7. That in needles from five to eight inches in length, 
their weights being equal, the directive forces are nearly as the 
lengths. — 8. That the directive force does not depend upon 
extent of surface, but in needles of nearly the same length and 
form, is as the mass.-^9. That the deviation of a compass- 
needle occasioned by the attraction of soft iron, depends, as Mr 
Barlow has advanced, on extent of surface, and is wholly inde- 
pendent of the mass, except a certain thickness of the iron, 
amounting to about two-tenths of an inch, which is requisite for 
the complete developement of its attractive energy.” 
8. Effects of Magnetism on Chronometers . — In our two pre- 
ceding Numbers, we have had occasion to direct the attention of 
our readers to the very interesting and valuable researches of 
Mr Barlow, respecting the effect of magnetism on chronometers. 
The following interesting anecdote relative to this subject, has 
been communicated to us by an [esteemed correspondent : 
When Harrison’s timekeeper was under trial at Richmond, 
it did not go as was expected. No one suspected the cause, 
till his late Majesty George TIT., who interested himself much 
about the machine, suggested that it was affected by a magnet 
which was lying near it. The magnet was removed, and the 
timekeeper recovered its rate.” 
ELECTRO-MAGXEXISM. 
9. New Electro-Magnetic Apparatus. -^Mx Faraday of the 
Royal Institution, has recently constructed a new apparatus for 
the revolutions of the wire round the pole, and a pole round the 
wire. ‘‘ When Hare’s calorimotor was used to connect with it, 
the wire revolved so rapidly round the pole, that the eye could 
scarcely follow the motion, and a single galvanic trough, contain- 
ing ten pair of plates on Dr Wollaston’s construction, had power 
