458 Scientific Proceedings^ Royal Dvhlin Society. 



or less the barometric pressure at the place of their source. Of small 

 quantities given off probably no account could be taken, since 

 their influence on the barometer would be insignificant; but for 

 great quantities of gases given off the effect would be all the more 

 marked, proportionally to the volume, temperature, power of dila- 

 tation, and lowness density of such gases, since ascendant currents 

 must then arise with consequent fall in the barometer. Therefore 

 there may be cases where a fall in the barometer would really and 

 truly serve as an indication of an impending earthquake, but would 

 also imply an escape of gases on a very large scale. This con- 

 nexion goes far to explain also many manifestations frequently 

 recorded as following on or accompanying earthquakes, such as 

 sudden whirlwinds or local storms, great electrical tension and 

 display of lightning, balls of fire or meteors, and even the so fre- 

 quently-mentioned seasons of disease or bad harvests, since great 

 quantities of noxious gases thus poured out from the earth would 

 necessarily saturate the pores of the earth, be retained there, and 

 consequently influence both vegetable and animal life,. We know 

 little yet as to the constitution of the atmosphere at heights such 

 as 10,000 m. above the sea level, or even, indeed, between 8000 

 and 10,000 m. ; but it has been distinctly ascertained that the 

 quantity of ammonia increases with height, while the carbonic acid 

 decreases ; and we may therefore assume that hydrogen and the 

 volatile carbides of hydrogen increase in quantity also with height 

 where they are subjected to the action of electricity and solar action, 

 giving rise thus to combinations accompanied by emissions of light 

 such as to present the appearances of meteors. Is there not some 

 similarity between the conditions presented by the highly rarified 

 atmosphere at those heights and those presented by the vacuum 

 tubes experimented on by Crookes, by means of electrical currents ? 

 This idea of foreseeing earthquakes, by the careful observation 

 of all the phenomena connected with them, is one involved in 

 De Rossi's proposed seismical and endodynamical map of Italy. 

 In the address alluded to he commences by calling attention to 

 one of the results of his studies, that is, " that we always find a 

 certain identity as regards the manner and the quality or energy of 

 action of all the earthquakes which in the course of time have af- 

 fected or affect a given locality ; whence follows the possibility of 

 affirming that with the aid of certain geological and orographical 



