100 T. C. Mendenhall — Seismoscopes and 



merit of a plan of attack and the selection of the most desirable 

 regions for the inauguration of the work. A scale of intensities 

 was adopted and a series of questions formulated which were 

 printed in the form of circulars for distribution among the in- 

 telligent observers of any disturbance. These circulars were 

 subsequently made use of by Captain Dutton, who had the gen- 

 eral direction of the work, and considerable information con- 

 cerning several earthquakes has been obtained. The Charleston 

 earthquake of 1886, renewed and greatly increased the interest 

 in the problem. It was thoroughly investigated bj Dutton and 

 Hayden and their report* upon it, presented to the National 

 Academy of Sciences in April, 1887, is of great value. As 

 complete, perhaps, as was possible under the circumstances, it 

 serves to emphasize the necessity for the use of seismic appa- 

 ratus, and causes extreme regret that instruments had not been 

 previously perfected and put in operation. 



I think it can be said that America has made at . least one 

 really valuable contribution to the Science of Seismology. I 

 refer to the approximate determination of the velocity with 

 which earthquake waves are transmitted through the crust of 

 the earth. The unexampled opportunities offered in the explo- 

 sions at Hell Gate and Flood Rockf were utilized for this pur- 

 pose, with the unexpected and surprising result of a rate of 

 transmission vastly greater than that previously obtained by 

 European and Oriental Seismologists, and generally accepted as 

 fairly accurate. The reduction of fairly accurate time observa- 

 tions made on the occasion of the Charleston Earthquake,;}: 

 served to confirm this conclusion and a speed of several thou- 

 sands instead of a few hundreds of meters per second must now 

 be admitted. Although these results are more nearly in accord 

 with the theory of wave transmission, future determinations of 

 velocity will be awaited with great interest, and all processes 

 employed must be carefully scrutinized. 



Before considering a plan for the inauguration and main- 

 tenance of an extensive series of seisomological observations, it 

 will be well to inquire what knowledge is most desirable in 

 the interests of geological investigation. This is a question 

 for geologists to answer ; but I venture the assertion that in 

 the present state of our knowledge of seismology, it is most 

 desirable, in the case of any given earthquake, to be able to 

 fix the seismic vertical, or the epicentrum; to ascertain the 

 depth at which the initial disturbance occurred ; and to 

 measure the velocity with which the resulting waves are 

 transmitted. If these can be accurately determined for differ- 

 ent earthquakes, under varying conditions, some light may be 



* Science, May 20th, 1887. f Science, Jan. 8th, 1886. 



\ Science, May 20th, 1887 ; see also this Journal, Jan., 1888, pp. 1-15. 



