THE RECENT ADVANCE IN. SEISMOLOGY 307 
words of Milne uttered twelve years earlier.‘ Today seismologists 
have so perfected recording instruments that at all first-class stations 
they are able to report great earthquakes which have occurred any- 
where upon the globe, and less than a half-hour after their occurrence, 
the news having been telegraphed to them by the earth itself through, 
it may be, its entire diameter; and to have their reports confirmed by 
the telegraphic cables some hours or days later, according as cables 
have or have not been fractured. In his observing-station at Shide, 
upon the Isle of Wight, Professor Milne has been able to reassure 
anxious friends after the press announcement of a terrible earthquake 
in a nearly antipodal region, and confirm the fact from later press 
dispatches that the earlier report was a fabrication.? 
The possibility of fixing the location of the disturbed region in 
the case of one of these so-called “unfelt quakes” is inherent in the 
fact that the waves of macroseisms are transmitted apparently not 
only through the mass of the globe, but also along its circumference. 
Those waves which first reach the station, the “ preliminary tremors”’ 
of the seismogram (see Fig. 1), appear to come by the direct route 
through the earth’s mass, as is pretty clearly shown by their constancy 
of velocity when the station is distant, and their variability of speed 
when the disturbed district is near. For the long distances the 
velocity is quite uniform and about to kilometers per second, so that 
the diameter of the earth is traversed in about 20 minutes. 
The Japanese school of seismologists have generally held that 
the waves which produce these preliminary tremors in the seismogram 
r An excellent account of the growth of the new methods of study may be found 
in the paper by W. Schliiter, ‘‘Schwingungsart und Weg der Erdbebenwellen,” Bez- 
trdge zur Geophysik, Vol. V (1901), pp- 314-59. 
2 For a description of modern seismographs see C. E. Dutton, Earthquakes in 
the Light of the New Seismology (London and New York, 1904), in which the Italian 
instruments designed by Agemennone are described with especial fulness; C. F. 
Marvin, “‘The Omori Seismograph at the Weather Bureau” (Monthly Weather Review, 
June, 1903, pp. r-8) and ‘‘Improvements in Seismographs with Mechanical Registra- 
tion” (zbid., May, 1906, pp. 1-6), where the Borsch-Omori instruments with Marvin’s 
excellent improvements are described; A. Sieberg, Handbuch der Erdbebenkunde 
(Braunschweig, 1904), where the Wiechert Astatic Seismometer, the most modern and 
satisfactory instrument, though the most difficult to manage, is described and figured. 
Much may be learned from the trade catalogues of Spindler & Hoyer, of Gottingen, 
the manufacturers of the Wiechert instrument, and of J. & A. Borsch, 15 Miinster- 
gasse, Strassburg, the European manufacturers of the Omori type of pendulum. 
