ON THE FACTS OF EARTHQUAKE PHENOMENA. 15 
fixed upon it. Thus he says, let A represent the earth, whose surface, 
A 
DBI, is thrown up by-some force so as to assume the form between D and 
I of DCI; further, let there be two rods, DC, DB, jointed at D, which shall 
represent one-half of the elevated portion of the earth’s crust, viz. DC, DB. 
in the former figure. Now, he says, if motion towards and away from the 
rod A be given to the rod DC, round the point D, then will the pendulums 
fixed to the rod DC swing laterally. 
The question of partial elevations by earthquakes, and their presumed 
effects upon the length of the day at the place, are then discussed. The au- 
thor then proceeds to show how that, by the repetition of insensible pulses, 
motion may at last become sensible at a given point; from this, and from 
the (unhappy) assumption that all earthquakes vibrate from west to east and 
the contrary, which he admits to be an essential condition upon which his 
final conclusion depends, he proceeds to make out an imaginary theory to 
account for all earthquakes as being related to a sudden or partial cessation of 
the earth’s rotation, according to the Copernican view, taking care, however, 
to put in a precautionary clause, “ Salva quam ecclesiasticis statutis debeo 
reverentia.” On this conclusion we need make no remark, but in the au- 
thor’s own words, from his Epistle Dedicatory, “ Nempe quod cum isti tune 
crederent motum illum esse in suo capite, qui tamen fere erat in terra ipsa ; 
ego e contrario gyrum illum quem mihi videor in terra conspicere, totum in 
capite meo perpetior.” 
_ Although thus finally led off from all that is true in his subject and to 
an absurd conclusion, the work of Travagini is a truly remarkable one, from 
the peculiar inductive and experimental manner in which he treats a subject 
_ previously never regarded but as matter of the vaguest guessing, and from 
_ his appearing to be the first who obtained some imperfect glimpse of earth- 
_ quake motions being due to pulses, or wave forces, in solids. 
___ Hooke’s discourses of earthquakes were delivered before the Royal 
ἢ Society about 1690, and were published in his posthumous works, by 
_ R. Waller, Sec. R.S., in 1705, fol. Though called a discourse of earth- 
_ quakes, these lectures are, in fact, a sort of system of physical geology, in 
' which the forces, forms, conditions and effects of elevation of land are largely 
_ Considered, but in which the ingenious author loses sight perfectly of what 
_ an earthquake is, and systematically confounds all sources, sorts and degrees 
_ of elevatory forces and their effects, with the transient action and secondary 
effects of earthquakes as rightly defined. These lectures are a repertory of 
‘much valuable information and thought to the geologist, but add little 
_ indeed to the subject of their title. Hooke divides the effects of earthquakes 
into four sorts ; viz.— 
| 
The first sort or genus. 
1st species.—The raising a considerable part of a country which before 
