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of the wire being almost in contact with the surface of 
mercury contained in a smail metallic cup. The least vertical 
jar brings the lower point of the spring into contact with the 
mercury, thus completing an electric current and recording 
the signal. Although I adjust this so that I can scarcely see 
space between the end of the wire and its reflected image in 
the mercury, many sensible tremors occur which it fails to 
register. I find by experiment that tne floor of the room 
near the wall responds to a foot-fall through a space six 
times that for which the instrument is set as above, the floor 
being a good solid one; the actual measures of adjustment 
being ‘005in. for tremors, and ‘03in. for floor. 
I have now to describe what may be more properly 
designated as my seismometers. For horizontal earth-move- 
ment I have a free pendulum, with a bob of about 4b. 
weight. Projecting perpendicularly under the bob is a 
fine tube, in which slides a pin, point downwards. The 
point of the pin rests, by its own weight, upon the 
smoked surface of a piece of glass, which is elevated to 
the pin by three screws underneath. Any oscillation of the 
pendulum, or rather of the glass itself (as it is really the 
tablet, and not the style, that partakes of the earth motion) will 
of course record itself on the glass. The marks are afterwards 
measured by micrometer and the direction noted. By far 
the largest reading of this instrument was recorded on 13th 
July, last year; namely, 0°28in. (whole oscillation), the 
next largest being 0'09in. on 7th December, 1883. 
My vertical seismometer is on the same principle as the 
electric vertical signal (described before) namely, a weight 
suspended by a coiled spring. Between the spring and the 
weight is a horizontal lever, attached at one-fifth of its length 
from the pivotted end; the free end carrying a pin point 
which traverses the surface of a piece of smoked glass. The 
motion is thus multiplied 5 times. The highest reading of 
this instrument occurred on the same date as that of the 
other, being 0-15in., on 13th July, 1884. (This to be 
divided by 5 for actual motion). 
The transit instrument should be a most delicate indicator 
of any permament displacement. I have, from time to time, 
had to make minute readjustments, necessitated probably by 
the operation of the tremors. The cause is, however, uncer- 
tain, and the indications extremely minute. 
The Rev. Canon Brownrigg, by a fortunate chance, obtained 
an optical observation of one of these tremors in the telescope. 
He was observing a star, when he noticed that the image 
began to dance in the field of view. He was puzzled as to 
what had shaken the telescope, until, on going into the house, 
he learned that a shock had occurred at about the time he 
