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Mr. G. C. Lowe exhibited part of a mercurial seconds 
pendulum, which, from its mode of construction, bears a 
strong resemblance to a horse-shoe magnet, and possesses 
considerable magnetic power. It is what is called the stirrup, 
and has attached to its lower extremities a circular brass disc, 
upon which the jar of mercury is placed. The stirrup is 
attached to the lower end of the pendulum rod, and has two 
steel rods, about ten inches in length, connected at their upper 
ends by a short steel bar, so that when magnetised the lower 
ends form one a north and the other a south pole. It had been 
suggested by Mr. Baxendell that some irregularities which are 
observed in the rates of clocks may be explained by referring 
them to variations in the intensity of the earth’s magnetism 
influencing a pendulum which has thus become magnetised. 
Pie had noticed in two clocks which have mercurial 
pendulums sudden changes of rate amounting to nearly or in 
some instances quite one second per day. There were no 
considerable changes of temperature or of the atmospheric 
pressure at the time, and the compensation is so nearly 
perfect that so great a deviation from the rate could not be 
due to change of temperature. A very brilliant display of 
aurora borealis was observed by Mr. Baxendell on the evening 
when the last remarkable change of rate took place, which 
favours the view now suggested, viz., that the lower part of the 
pendulum having become magnetised, an increase or diminu- 
tion of the intensity of the earth’s magnetism may have the 
effect of accelerating or retarding the motion of the pendulum. 
Mr. Lowe suggested that if the rods forming the stirrup were 
connected with brass at the top instead of steel, they would 
have much less force as magnets. In a pendulum also under 
Mr. Baxendell’s observation, the disturbance of rate was 
much smaller in amount, scarcely exceeding one-third of the 
change that was found in the two clocks already mentioned. 
This pendulum consists of a long steel rod and two shorter 
ones, and has a very correct compensation effected by a zinc 
