ON THE FACTS OF EARTHQUAKE ΡΗΞΝΟΜΕΝΑ. 91 
transient effects of the earthquake which may result from such actions. 
_ He does not attempt to assign the law of motion of any one of the several 
_ orders or sorts of earthquake waves. The shocks, he says, are either hori- 
zontal and vertical, or rotatory and vorticose in direction; the two former, 
he says, are always observed together—the latter is rare ; several secondary 
effects of earthquake action, such as twisting of buildings or their parts, 
_ landslips, &c. he gives an erroneous account of. 
τ΄ But this is rather anticipating as to date: before concluding, however, the 
- in his 10th chapter an account of earthquakes, which, for his day, is lumi- 
_ nous and good. He briefly and correctly describes the principal phenomena; 
_ traces a distinct connection between volcanic and earthquake effects ; 
proposes the sudden evolution of steam by contact of water with igneous 
_ matter at great depths as the immediate cause of both ; conceives the horrid 
Moises as due to the rending of rocks or strata, and seems to have had some 
_ obscure notion that the internal heat of our planet might be independent of 
any form of combustion. : 
_ In 1835, a copious and exceedingly strange work, the ‘ Théorie des Vol- 
_ cans,’ par le Compte A. de Bylandt Palstercamp, appeared at Paris, 3 vols. 
0, with fol. atlas. 
We have here nothing to do with the author's singular attempt to build up 
a theory of volcanic action, indeed almost a cosmogony, from considerations 
derived from the relations and reactions on our planet, of light, heat, elec- 
- tricity and magnetism. With all its wildness and incoherence it carries per- 
haps a dim fore-shadowing of truth. 
In his first volume, p. 373 to 392, he devotes a section to the consideration 
of earthquakes, as derivative effects of volcanoes. This, like indeed every 
‘other part of the book, bears the peculiarity of containing some truths, or 
uasi truths, much in advance of the author's day, mixed with a great deal of 
absolute error. 
He clearly recognises earthquakes as merely one class of effects due to 
oleanic action ; but although he uses the word vibration, &c., and has even 
rrived at some of the phenomena resulting from wave motion clearly enough, 
5 obvious that he has formed no clear idea of pulses transmitted through 
ic media in virtue of the elasticity of the solids themselves ; his vibrations, 
their origin, are nearly analogous to those of Mitchell. Shocks or 
ws transmitted through and from cavities under the earth, suddenly filled 
or emptied of aériform fluids, which actually lift up and again drop down the 
lls of these cavities in rising and falling, originate and constitute Bylandt’s 
shock. So far, therefore, he is not beyond his predecessors. But further :— 
“Etablissons d’abord comme principe que les effets des tremblemens de 
terre sont toujours contradictoires aux causes qui les produisent, et dirigés 
5 le sens inverse, et que les mémes causes produisent des effets contra- 
ires dans les lieux opposés.” “Les causes des tremblemens de terre 
dent toujours dans lintérieure de la terre et 4 une certaine profondeur. 
en élévant une perpendiculaire du fond de cette profondeur et en trans- 
ttant le mouvement du point le plus bas au plus élévé, l’effet sera celui 
ἢ pendule, c’est-d-dire contradictoire entre les deux extremités. 
Lorsqu’on a senti 4 la surface une vibration ou oscillation dans la direc- 
