516 



SCIENCE 



[Vol. IV., No. 96. 



ation of the mesethmoid, rises above the plane 

 of the top of the skull, and extends forward 

 beyond the jaw. A bilateral expansion of its 

 base in front forms a firm supporting pad, 

 resting upon the pre-maxillary bones. The 

 two remaining cartilages are paired. 



Since returning from the seal-fishery, I have 

 examined the accessible works that would be 

 likely to mention this curious appendage, but 

 have failed to discover any thing approach- 

 ing an accurate or complete description of it. 

 That given b}- Fabricius more than a centur}^ 

 ago is one of the best All writers whose 

 accounts I have seen, including the most recent, 

 agree in failing to express the chief character- 

 istic of the animal, which is, that the so-called 

 ' hood ' of the male is an inflatable proboscis, 

 protruding considerably beyond the mouth, 

 which it overhangs. 



C. Hart Merriam, M.D. 



MEASURING EARTHQUAKES. 1 



In view of the recent earthquake in England, and 

 the still more recent shakings which parts of this 

 country have experienced, a notice of the above 

 work will be of especial interest. Professor Swing's 

 long residence in Japan as professor of mechani- 

 cal engineering in the University of Tokio, and his 

 active labors in connection with the Seismological 

 society there, of which he was vice-presi- 

 dent, entitle him to speak with authority 

 on this subject. Indeed, in this matter of 

 the exact measurement of the motion of 

 the ground during an earthquake, seis- 

 mologists the world over must look for enlightenment 

 to young Japan, whose Seismological society, under 

 the guidance of the foreign professors in her univer- 

 sity and her college of engineering, has in this partic- 

 ular branch far outstripped European seismologists. 



In chapter i. Professor Ewing gives a resume of 

 the theory of waves in an elastic solid, as applied by 

 Hopkins, in the British association report for 1847, to 

 the case of terrestrial disturbances; "since it both 

 teaches the earthquake-observer what to look for, 

 and guides him in the interpretation of his results." 

 This shows how, from a single sudden disturbance, 

 two series of waves will set out in all directions, — the 

 first or normal waves consisting of compression and 

 expansion of the material in the direction of transit; 

 the second or transverse waves travelling more slow- 

 ly, and consisting of motion of distortion at right 

 angles to the line of transit, — also how these waves 

 may be reflected or refracted at the bounding-sur- 

 faces between different strata, and thus by successive 

 reflections be reduplicated ; so that, at a distant point, 



1 Memoirs of the science department, Tokid Daigaku ( Uni- 

 versity of Tokid), No. 9. Earthquake measurement. By J. A. 

 Ewing, B.Sc, F.R.S.E. Tokio, Tokid Daigaku, 1883. 12+92 p., 

 23 large plates. 4°. 



the vibrations will probably be far different from 

 (in number, order, phase, and period), and generally 

 much more complicated than, those at the origin. 

 Add to this the effect of imperfect elasticity, and the 

 condition that the original disturbance may he a 

 series of slips along a whole line or ' fault,' and noth- 

 ing further could be desired to give confusion to the 

 vibrations. 



Chapters ii. and iii. deal with instruments for 

 measuring the horizontal motion of the ground. At 

 the outset Professor Ewing notes the difficulties in 

 the way of getting a steady point, or something ' to 

 tie to,' while every thing around is being shaken ; and 

 the characteristic feature of every seismometer is its 

 method of supporting a heavy mass so that it will 

 remain steady, receiving no impulse (save what is 

 unavoidable through friction) while the system that 

 supports it is being shaken. As the ' horizontal pen- 

 dulum ' seismograph in one of its forms is considered 

 the best, and has given the greater part of the records 

 obtained, its essential feature is here shown in fig. 1. 

 Popularly it might be termed a heavy weight, swing- 

 ing on a gate. It is a heavy mass, pivoted upon a 

 vertical axis through d, upon a frame free to move 

 about the vertical axis be. The long light reed mul- 

 tiplies the motion, and records it upon a rotating 

 smoked-glass plate by the steel pointer on its end. 

 This reed is pivoted at d, with most of its weight 

 taken up by the coil-spring, whose tension is adjusta- 

 ble at e. The parts of this supporting lever and long 

 reed are so proportioned that in the vertical axis 

 through d lies the centre of percussion relative to the 

 axis be : hence, if this is shaken through be at right 



Fig. 1. 



angles to the plane of the lever, the vertical through 

 d will be of itself the axis of instantaneous rotation, 

 independent of the heavy mass pivoted there; hence 

 the latter will receive no impulse at right angles to 



