Seismological Investigations. 109 



we at once meet with the difficulty of properly illuminating the 

 face at night. 



Among other methods which have been proposed, probably 

 the most simple is that of Milne,* which consists in placing 

 small pieces of cork, coated with an oily ink, upon the extremi- 

 ties of the hands of the clock against which a paper or card 

 board ring is pressed by electro-mechanical devices, put in 

 operation by the closing of the circuit at the seismoscope. 

 After an instant of pressure the ring is withdrawn, bearing a 

 printed record of the position of the hands of the clock. This 

 allows the determination of the error and rate of the clock 

 either before or after the earthquake or both, and should the 

 clock be stopped by a violent shock, the time record is not lost. 

 These advantages will undoubtedly lead to the invention of 

 simple and sure methods by means of which this printed record 

 may be obtained. For stopping a clock, Milnef has used a thin 

 piece of board in which notches are cut in one of which the 

 pendulum is caught at the moment of the disturbance. This 

 method is likely to allow and sometimes to cause considerable 

 subsequent swaying of the pendulum and I have preferred to 

 use simply a strip of brass, curved to an arc of the circle whose 

 radius is the pendulum. This lies always nearly touching the 

 pendulum and is slightly lifted when the circuit is closed so 

 as to arrest the pendulum. The brass strip is attached to the 

 movable armature of a common telegraph sounder secured to 

 the side of the clock case. The circuit remaining closed after 

 the action of the seismoscope the pendulum is held in its place. 



Application. 



Two seismic stations with time-taking apparatus have been 

 in operation in this country for nearly a year. The first was 

 established in the Physical Laboratory of the Signal Office in 

 Washington shortly after the occurrence of the Charleston 

 Earthquake, and the second, at the Rose Polytechnic Institute, 

 Terre Haute, Ind., was put in operation in January, 1887. 

 Both are equipped with seismoscopes similar to that described 

 and shown in fig. 1 and with clocks known as " Regulator No. 

 2," made by the Seth Thomas Co. These clocks were selected 

 on account of their cheapness and their really excellent perform- 

 ance as time keepers. The stopping apparatus is of the simple 

 form already described, and an ordinary vibrating electric bell 

 with battery is connected with it so that a continuous alarm is 

 maintained from the time of the disturbance of the seismo- 

 scope. 



* Trans. Seis. Soc. Japan, vol. iv. f Trans. Seis. Soc. Japan, vol. iii. 



