94 
that artificial earthquakes could be produced by exploding 
dynamite in holes inthe earth. When a miner fired a blasting | 
charge in a mine he produced an earthquake on a small scale. 
The greater number of these explosions, said Professor Milne, 
“take place beneath the sea, and are probably due to the 
admission of water through fissures to the heated rocks 
beneath.” Comparatively recently it has been discovered that 
the earth’s crust is in a constant state of tremor. These vibra- 
tions could only be detected with instruments of great delicacy 
and to those instruments the microphone had now been added. 
The first person to adopt the microphone for seismic obser- 
vation was an Italian professor, by the name of Rossie. He 
found that the tremor at times increased in violence, and 
sometimes their maximum resulted ina sensible earthquake. 
It was suggested that the sounds heard by means of the 
microphone were the explosions which produced the tremors, 
and, when in sufficient force, an earthquake. One important 
matter in connection with these tremors was that they appear 
to be influenced by a falling barometer in a marked manner. 
It had been contended by some writers that volcanic eruptions 
and earthquakes were influenced by the weather, and likewise 
by the moon. It could not be disputed that the weight on 
the crust of the earth was increased or lessened according as 
the barometer rose and fell. He could not however regard the 
weather influence as more than secondary, and not as the 
primary cause. If there happened to be a great stress below a 
portion of the crust due to those agencies which produce 
seismic disturbance, then a fall of the barometer might bring 
matters to a crisis. On this point however more information 
was required. It was true that the New Zealand eruption 
was preceded by a fall of the barometer. He had not seen any 
reliable reports of the position of the barometer along the 
Mediterranean previous to the recent earthquake there, but 
they had the fact that very extraordinary weather had prevailed 
over Europe of late. The causes which regulated the seasons 
were little understood, and possibly it may be discovered that 
these causes may have also an influence on seismic phenomena. 
