66 



REPORTS ON THE STATE OP SCIENCE. 



XIII. Sensibility of Seismographs recording on Smoked Surfaces. 



On several occasions in the British Association Eeports I have given 

 illustrations of the marked want of sensitiveness of seismographs which 

 record on smoked surfaces. 1 Instruments which work in this manner 

 are inexpensive to maintain, you can at any time see your record, and 

 they yield most excellent seismograms of strong disturbances. How- 

 ever, in consequence of the elasticity of the writing levers, and possibly 

 for other reasons, they do not commence to give a record until a certain 

 amplitude of motion has been reached. They therefore fail to record 

 minute movements, and as these may frequently represent that which 

 remains of an earthquake originating at a great distance, those who use 

 these types of instrument are entirely cut off from what I have called 

 a ' New Departure in Seismology. ' As bearing upon this point I give 

 the following quotations from the report of the Director, Bombay and 

 Alibag Observatories, 1910. The italics are mine: — 



Milne's Seismograms, 

 photographic Re- 

 cords. 



Vertical movement 

 Seismograms. 



There was no loss of 

 record. 



Cola .ba No. 1 (E.-W. 

 Seismograms. 



Colaba No. 2 (N. 



Seismograms. 



S.) 



Omori Seismograms. 



Out of 9 principal dis- 

 turbances 7 were re- 

 corded and 1 was not 

 recorded. 



Out of 48 small disturb- 

 ances 20 were recorded 

 and 26 were not re- 

 corded. 



Out of 9 principal dis- 

 turbances 8 were re- 

 corded. 



Out of 48 small disturb- 

 ances 37 were recorded 

 and 8 were not recorded 



Out of 9 principal dis- 

 turbances 8 were re- 

 corded. 



Out of 48 small disturb- 

 ances 31 were recorded 

 and 13 were not re- 

 corded. 



Out of 9 principal dis- 

 turbances all were re- 

 corded. 



Out of 48 small disturb- 

 ances 36 were recorded 

 and 11 were not re- 

 corded. 



The action of the instrument is 

 voluntarily interrupted, e.g., 

 for regular changing of the 

 tilrn, winding and rating the 

 watch and clock, adjustment 

 and examination of the instru- 

 ment, deflection experiments, 

 &o. ; such interruptions are 

 not taken into consideration. 



1 disturbance was partially lost 

 in shifting time. 



2 disturbances were lost as the 

 paper did not come out. 



1 disturbance was partially lost 

 in shifting time. 



2 disturbances were lost in 

 shifting time and 1 was lost 

 owing to the smoked paper 

 being destroyed. 



1 disturbance was partially lost 

 in shifting time. 



1 was lost owing to the stoppage 

 of clock ; 2 were lost in 

 shifting time, and 1 was lost 

 owing to the smoked paper 

 being destroyed. 



1 was lost owing to tho smoked 

 paper being destroyed. 



1 See Brit. Assoc. Seis. Reports, 1909, p. 51, 'Aftershocks of the Earthquake at 

 Jamaica '; 1910, p. 48, 'A New Departure in Seismology. 1 



