HERTFORDSHIRE EARTHQUAKES. 163 



their part in contributing data that will help to determine the 

 genesis of seismic phenomena. Until we possess a more perfect 

 knowledge of the physical conditions existing a few miles 

 beneath the Earth's crust, we should be content to be tentative 

 and not dogmatic in our assertions." 



(Whilst this paper was being passed through the press Dr. C. 

 Davison has informed me that a doctor who was at Valparaiso at 

 that time told him that " a curious light played along the tops 

 of the mountains at the time of the earthquake." This Hght 

 is referred to in the TweKth Report of the Seismological Com- 

 mittee of the British Association, where the following occurs : — 

 " Accounts of luminosity in the heavens or on hills at the time 

 of large earthquakes are common. One of the last occasions 

 upon which phenomena of this nature were observed was at the 

 time of the Valparaiso earthquake, August 17th, 1906," when 

 " there appeared upon the liills at a height of about 500 metres 

 waves of light. These waves, which are compared to chain 

 lightning, extended as far as the eye could reach, and lasted 

 during the first shock, or nearly two minutes. On these 

 occasions strong earth-currents have affected the working of land 

 lines, and needles of galvanometers have been disturbed." 



Dr. John Milne, Secretary of the Seismological Committee, 

 noticed that a quarry in the Isle of Wight, known as Pan 

 Chalk Pit, appeared from time to time to be luminous. This 

 induced him to carry on a series of experiments in the hope of 

 throwing some light upon the subject. He foimd that bromide 

 photographic paper placed underground in the chalk and care- 

 fully excluded from light was at times curiously affected as by 

 hght, while it was not so affected in the same apparatus when 

 above the ground, and he was led to make the suggestion that 

 the markings " may result from very feeble brush or glow-light 

 electrical discharge. If this be so," he says, " it would also 

 account for the bands on the photographic paper, the other 

 markings being due to minute sparks."* Thus it would appear, 

 as he infers, that there are radio-active or electrical emanations 

 from oiu' earth. Of sixty-three earthquakes recorded by his 

 seismograph at Sliide during these experiments, only ten nearly 

 coincided with the times of occurrence of spots upon the paper, 

 and he regarded these coincidences as accidental. A probable 

 cause is therefore disclosed of certain luminous phenomena 

 sometimes observed dvu^ing earthquakes, although these experi- 

 ments have not resulted in any connection being traced between 

 them.) 



IV. CONCLTJSION. 



Electricity is merely a form of energy inseparable from 

 matter. Some even attribute to it the origin of matter. 

 Produced as it can be by friction, it may be converted into 



* The Report of the Seismological Committee, giving a full account of the 

 experiments, will appear in the Report of the British Association for 1907. 



