538 



NA TURE 



[October 13, 1923 



Lenard's observations and his own experiments into 

 account, Dr. Simpson concludes that it is not an 

 induced effect, due to an external source ; he con- 

 siders that there is an actual pro<luction of electricity 

 in the subdivision of large raindrops. 



Dr. Simpson's conclusion has long been in my mind. 

 Latterly, the subject has been an attractive one to 

 me, on account of the views I have formed of the com- 

 position of water and of the chemical changes attend- 

 ing alteration in the size of drops, referred to in my 

 recent communication to the Koyal Society (Hoy. Soc. 

 Proc. A, vol. 103, p. 616, 1923). I was much impressed 

 by a lecture at the Royal Institution given early in 

 the year by Dr. Simpson (Nature, April 14) ; this, 

 together with a violent hail-thunderstorm which I 

 experienced while yachting in August, led me to look 

 more closely into the problem. 



Assuming that water be the cause, the view I should 

 be inclined to take is the converse of that advocated 

 by Dr. Simpson. Granting, for the sake of argument, 

 that changes in water can give rise to free electricity, 

 the fusion of small drops into large would seem to be 

 the more likely process — this being a positive change, 

 in the sense that energy is liberated, while the division 

 of large drops should involve a loss of energy. I 

 assume that the small drops are richer in hydrone than 

 the larger and that changes in composition of the 

 water take place such as I have postulated in my 

 recent communication. 



Going further, however, can it be granted that 

 chemical changes in a wholly liquid circuit ever give 

 rise to sensible electricity — must not the circuit be 

 tapped by conducting electrodes to make this obvious ? 

 We must assume that the interactions are primarily 

 electrolytic, but is not the electrical energy, in such 

 cases, always lowered into heat energy ? 



The question is of fundamental importance, and it 

 is on this account that I make bold to be critical of 

 a solution of a problem outside my field ; yet it is one 

 of the borderland issues which chemist and physicist 

 should jointly consider. 



Assuming that my interpretation be correct, may 

 not the great rise in potential required to produce 

 lightning have its origin in the coalescence or co- 

 operation of minute drops charged by an external 

 source ? 



Lenard {Wied. Ann., 1892, 46, p. 584) dealt with the 

 effect, in the first instance, in studying the electricity 

 of waterfalls. His later laboratory experiments led 

 him to the conclusion that it was due to the impact of 

 separate drops upon a flat surface. The water was 

 allowed to splash into a zinc tray. Both he and Dr. 

 Simpson found it necessary to use distilled water ; 

 that from the mains gave little or no result. The air 

 potential observed was negative, but with a solution of 

 salt it was slightly positive. Up to a certain point, 

 the potential increased rapidly with the length of the 

 jet. Various liquids other than water were tried : 

 the potential varied in sign and magnitude, but the 

 effect was sUght as compared with the water effect. 

 Lenard seems to think that the effect has its origin in 

 a contact difference of potential between gas and 

 liquid. All seems to me to point to chemical inter- 

 change being at the root of the phenomena and that 

 it is not a mere water effect. 



Henry E. Armstrong. 



Earthquake Warnings. 



The recent disaster in Japan demonstrates the 

 importance of endeavouring to ascertain if there are 

 any premonitory indications of a coming earthquake 

 shock which can be recognised and thus enable a 

 warning to be given of its approach. 



NO. 2815, VOL. I 12] 



It seems probable that the rupture, whatever its 

 nature may l)e. that gives rise to the actual vibratory 

 shock of an earth(]uake is preceded by a strain or 

 distortion of the earth's crust, which gradually 

 increases till the stress that causes it is suddenly 

 released. The existence of this strain should be 

 evidenced by a progressive .sag or tilt of the si ' 

 local and minute in amount, no doubt, but pr^ 

 sufficiently large to be detected. 



In the Milne-Shaw seismometer the vibrations 

 proceeding from distant earthquakes are recorded on 

 sensitised paper on a rotating cylinder by a spot of 

 light reflected from a mirror coupled to the Ixxjm of a 

 horizontal pendulum. Ordinarily it is only these 

 vibrations that are taken into consideration, but the 

 same instrument will also indicate a slow tilt of the 

 ground, provided that the exact position of the spot 

 of light can be recorded and measured. In some 

 instruments recently constructed, one of which b 

 being installed in Uganda, this is effected by the use 

 of a second, stationary mirror, which throws another 

 spot of light in a fixed position on the cylinder, and 

 traces a straight line on the record. If there i.s a tilt 

 of the earth's surface it will be indicated by a variation 

 in the distance between the mean position of the line 

 due to the moving mirror from that of the line due to 

 the fixed mirror, unless of course the tilt is in a 

 direction parallel to the horizontal pendulum. Such 

 an instrument is capable of showing a tilt of ,S" by a 

 movement of the indicating spot of light through i mm. 

 If two instruments are employed with their horizontal 

 pendulums at right angles to each other the direction 

 and amount of the tilt will be exactly determined. 

 Near the sea the rise and fall of the tide causes a slow 

 tilt and other changes of a slow periodic character 

 are known, but these can be allowed for and could 

 easily be distinguished from a progressive movement 

 indicating the approaching occurrence of an earth- 

 quake in the neighbourhood. 



It seems very desirable that such instrument 

 should be installed in localities which are known to be 

 subject to earthquakes. 



If it be found that shocks are in fact heralded by a 

 definite tilt, it may be possible to arrange for an electric 

 bell to attract the attention of the observer when such 

 a tilt occurs. If he is satisfied that there is sufficient 

 evidence of an approaching earthquake, a general 

 alarm can be sounded. In this way a warning might 

 be given several hours, or even days, before the shock 

 occurred. John W. Evans. 



Imperial College of Science and Tecl1n'■'""^• 

 S. Kensington, S.W.7. 



Human Embryology and Evolution. 



In his reply to Prof. MacBride (Nature, Sept. S) 

 Sir Arthur Keith states that in his Huxley lecture he 

 neither affirms nor denies the doctrine of use-inherit- 

 ance, but that he does deny that Lamarckism has 

 had no part in the evolution of man. If these words 

 were to be taken literally as expressing Sir Arthur 

 Keith's meaning, he and I would be to a great extent 

 in agreement, but it is obvious that the double 

 negative was an accidental mistake, and that Sir 

 Arthur Keith meant to deny that Lamarckism had 

 any part in the evolution of man. 



I have read the report of his Huxley lecture to the 

 medical students of Charing Cross Hospital Medical 

 School (Nature, Aug. 18), and it seems to me difficult 

 for an evolutionist to follow his train of thought or 

 reasoning. He does not distinguish between the 

 development of the individual and the evolution of 

 the race, between ontogeny and phylogeny. He 

 discusses the manner in which adaptations appear 



