Earthquake-wave Transit. 361 



itself — the duration of sensible disturbance as seen in the in- 

 strument being much dependent upon the dimensions, form, 

 material, and other details of construction of the mercury- 

 trough and other parts of the instrument. All the observa- 

 tions of velocity of wave-transit referred to by General Abbot 

 were made in completely discontinuous material, or in rock 

 more or less water-logged, and with the directions of stratifi- 

 cation, lamination, and Assuring imperfectly known and not 

 recorded. 



If General Abbot will refer to mv experiments at Holy- 

 head (Phil. Trans. 1861 & 1862), he will find the enormous 

 retardation of transit-velocity produced by Assuring and dis- 

 continuity, amounting in some instances to an extinction of -£- 

 of the velocity in the material of the rock if perfectly uufis- 

 sured. The velocity of wave-transit, therefore, in absolutely 

 discontinuous shingle can be but a small fraction of that which 

 •the material of the shingle itself could transmit. General 

 Abbot may satisfy himself of this by experiment upon this 

 shingle by methods altogether independent of the use of the 

 seismoscope. The velocity recorded in observation No. 5 — 

 5309 feet per second (Amer. Journ. p. 179), cannot, as it 

 seems to me, have been derived from the discontinuous shingle, 

 and seems more likely to be an over-rated velocity of the wave 

 derived from the water itself. Yet the velocities supposed to 

 be obtained approach, in most instances, those given as the 

 results recorded by the greatest experimental physicists for 

 the velocities of sound in media as uniform, dense, and elastic 

 as are many metals. If General Abbot will consult the works 

 of Wertheim, of Biot, not to name other renowned physicists, 

 and will compare the sound-velocities in solids as given by 

 them with those recorded in relation to the Hallet's-Point 

 experiments, I think he will see grave reason for doubt, at 

 least, as to the validity of the latter. To me, indeed, it seems 

 that, if they are to be accepted without further and radical 

 modification or explanation, we must cast aside nearly all that 

 has been accepted and is still held true as to the doctrine of 

 sound by all men of science since the time of Newton ; we 

 must also cast aside the deductions, as to the rate of transit of 

 earthquake-shock, derived from observation by Professors 

 Schmidt and Noggerath in earthquakes extending over large 

 areas in Hungary and in Rhenish Germany, as well as those 

 by myself of the great Neapolitan shock of 1857. Omitting 

 the last, as the time-measures were not free from doubt in 

 some instances, those of Schmidt and Noggerath may be relied 

 upon as made with much care and exactitude. All these 

 results square as nearly as was to be expected with those of 



