January 13, 1898J 



NATURE 



247 



quake ? The earthquake-hunters of Japan, no doubt, saw 

 a little that was before them ; but now, when they stand 

 beside the elaborate seismographs of the present day, 

 costing 50/. or loo/., and look backward upon the days 

 when pins were propped up in rows to act as seismo- 

 scopes, and twopence would buy a bit of string and a bob 

 for a pendulum, I do not think that it was ever anti- 

 cipated that the study of earthquakes would lead to the 

 knowledge which we now possess. 



In seismometry we have seen the gradual evolution of 

 several types of instruments which give faithful records 

 of the amplitude, period, duration, and the time of occur- 

 rence of all ordinary earthquakes. 



For this work we are greatly indebted to Ewing and 

 Gray, and it is fair to say that the seismometry of Japan has 

 done much to revolutionise seismometry throughout the 

 world. The examination of earthquake records completely 

 changed our ideas of earthquake motion, and we learned 

 that nearly all the formulae which up to this time had been 

 employed to calculate earthquake elements had been 

 founded upon a wrong hypothesis. The fact that the 

 period of earthquake motion increased as it died out and 

 as it radiated, coupled with a discussion of the observa- 

 tions made upon the movements which had occasionally 

 been observed in the bubbles of levels, magnetographs, 



Fig. I. — Static diagram of the earthquake of July 19, 1891, showing the 

 complicated direction of motion common to most earthquakes. (Milne.) 



and other instruments, and, above all, that now and then 

 unfelt earthquakes had been recorded, enabled one in- 

 vestigator to state, fifteen years ago, that it was " not 

 unlikely that every large earthquake might with proper 

 instrumental appliances be recorded at any point on the 

 land surfaces of our globe " — a prediction which of late 

 years has been amply verified. 



It was found that modified forms of seismographs 

 might be used to record the joltings of a railway 

 carriage, and thus to indicate defective points along a 

 railway line. Another application of seismometry has 

 been to measure the steadiness of a locomotive, which in 

 part depends upon the manner in which it is balanced. 

 On Japanese railways this has been turned to practical 

 account, with the result that a saving of from i to 5 lbs. 

 of coal per mile per locomotive has often been effected. 

 The modern seismograph is also used to measure the 

 elastic vibrations of bridge work, buildings, and steam- 

 ships. 



The greatest material benefits which recent seismo- 

 logical investigation has conferred upon the world are 

 those which have resulted in minimising the destruction 

 of life and property. The builder now, rather than 

 making a structure strong because an earthquake is 

 strong, has before him definite measures and a clear 



NO. 1472, VOL. 57] 



knowledge of the character of the forces he may expect 

 to meet. Given the dimensions and tensile strength of a 

 body that has been overturned or shattered, we can 

 calculate the maximum acceleration to which the same 



Fig. 2.— Earthquake of June 20, 1894, recorded at the Science College of 

 the University of Japan. The upper figure is the S.E.-N.W. com- 

 ponent ; the middle, the N.E-S.W. component showing preliminary 

 vibrations, the shock, and concluding vibrations ; and the lower, the 

 vertical motion. The intervals are the seconds of time. (Ewing's 

 Seismograph.) 



has been subjected, and that quantity is practically 

 identical with that derived from a seismogram. 



By experience we know the maximum acceleration 

 which may be expected in a given district or on a given 



Fig. 3. — The fore and aft motion of a locomotive as balanced in England 

 and after rebalancing in Japan, bj- which a safe speed has been increased 

 from 28 to 35 miles per hour, and coal saved. (Macdonald.) 



site, and we can therefore proportion a structure to meet 

 the known conditions. 



The fact that the new rules take into consideration 

 that buildings have to withstand measurable stresses, due 



