34 REPORTS ON THE STATE OF SCIENCE. — 1919. 



were furnished with these. They do not, however, give the earth 

 tides, and, like all other seismographs, they do not give a precise 

 reproduction of the earth movement. This was recognised by Galitzin, 

 and, shortly before his death, he brought out his new apparatus for 

 measuring the acceleration of the ground directly, by using the piezo- 

 electric property of quartz. Whether these instruments will do for 

 continuous seismometry remains to be proved. There are, however, 

 other methods, and there is ample scope for work in this direction. 



As the question of instruments is so essential to progress in obtain- 

 ing records in the simplest form, I may be permitted to add some 

 remarks on a subject so frequently ignored. 



In the initial search for a new effect one works rather in the dark, 

 and it is simply a question of getting an effect at all. But when we 

 have obtained some idea of the order of magnitude, and especially of the 

 time element of change, the suitable instrument for measuring it is 

 not a mere accident, but a matter for scientific design. 



A seismometer being essentially a pendulum, and the disturbance 

 due to an earthquake a complex phenomenon, the instrument in general 

 gives a record which is neither displacement, velocity, nor accelera- 

 tion, but a mixture, while some parts of the disturbance are exag- 

 gerated relative to others. Strict aperiodicity is a great help, and, in 

 my view, essential. And here may I enter a protest against the 

 frequent application of the term ' dead-beat,' which is really the same 

 as aperiodic (and has a precise quantitative signifacance), to cases where 

 large damping of indefinite amount is all that is meant? 



The primary period of the apparatus is a very important element in 

 an instrumental record, so that an apparatus suitable for giving the 

 long-wave phase of an earthquake may not be so suitable for the first 

 phase. 



In conclusion, it appears that there is ample scope in the future 

 for: — 



(1) The scientific design of apparatus suitable for recording the 



various movements of the earth. 



(2) The establishment of even a few first-order stations, one in 



each of the principal countries of the Empire, for record- 

 insf all three components of motion with a view to a deter- 

 mination of the mechanical properties of the interior of 

 the earth. 



(3) The establishment of a larger number of second-order stations 



for the investigation of local earthquakes. 



(4) Theoretical investigation of the form and stability of the 



crust, and the propagation of wave motion throughout 

 the interior. 



