68 MR. BROOKE ON THE AUTOMATIC REGISTRATION OF MAGNETOMETERS. 
The most violent shock that has been recorded, fig - . 10, Plate VII., occurred between 
5 h and 6 h on the 1st of April. On this occasion, the magnet, after suffering two small 
shocks, was at 5 h 20 m suddenly displaced as by a blow, and thrown into a wide oscil- 
lation, from which it did not return to a state of rest for 25 m ; it then sustained a 
considerable shock in the opposite direction, from which it again returned to a state 
of rest, in nearly its original position, about 6 h . 
It is confidently anticipated that a continuance of these observations during the 
approaching period of the year, when disturbances are usually most frequent and 
considerable, may lead to some interesting results. 
distinctness. By this means half the trouble of changing the papers and developing the impressions is saved, 
and the relative positions at intervals of 12 hours may be determined with a much greater degree of certainty, 
the only source of error being in reading the position of the edge of the lines on a scale. — May 1847. 
29 Keppel Street, 
June 16, 1846. 
