20 EARTHQUAKES. 



of apparatus forming the well-known seismograph of 

 Palmieri. 



Pendulum instruments, —Mallet speaks of pendulum 

 seismoscopes and seismographs as ' the oldest probably of 

 seismometers long set up in Italy and southern Europe.' 

 In 1841 we find these being used to record the earthquake 

 disturbances at Comrie m Scotland. 



These instruments may be divided into two classes : 

 first, those which at the time of the shock are intended to 

 swing, and thus record the direction of movement ; and 

 second, those which are supposed to remain at rest and 

 thus provide ' steady points.' 



To obtain an absolutely ' steady point ' at the time of 

 an earthquake, has been one of the chief aims of all recent 

 seismological investigations. 



With a style or pointer projecting down from the 

 steady point to a surface which is being moved back- 

 ward and forward by the earth, such a surface has written 

 upon it by its own motions a record of the ground to 

 which it is attached. Conversely, a point projecting up- 

 wards from the moving earth might be caused to write a 

 record on the body providing the steady point, which in 

 the class of instruments now to be referred to is supposed 

 to be the bob of a pendulum. It is not difficult to get a 

 pendulum which will swing at the time of a moderately 

 strong earthquake, but it is somewhat difficult to obtain 

 one which will not swing at such a time. During the 

 past few years, pendulums varying between forty feet in 

 length and carrying bobs of eighty pounds in weight, and 

 one-eighth of an inch in length, and carrying a gun-shot, 

 have been experimented with under a great variety of 

 circumstances. Sometimes the supports of these pendu- 

 lums have been as rigid as it is possible to make a struc- 

 ture from brick and mortar, and at other times they have 



