August 1 6, 1883] 



NA TURE 



36? 



Disease of Potatoes 



The ScUrotia referred to by Mr. Worthington G. Smith (in 

 Nature, vol. xxviii. p. 299) as having destroyed the potatoes 

 in Norway have been sent to me from two different places on our 

 western coast. As I usually travel every summer, I had no 

 opportunity of cultivating them myself ; so I sent them to Prof. 

 De Bary of Strasburg, who kindly informs me that he has 

 cultivated them with success. They belong to Ptziza sclero- 

 tiortim (Lib.). The spores of our Norwegian Peziza will pro- 

 duce Sclcrotia, as he has proved by experiment, also in Daucus 

 earola, and very likely in Phaseolus and some other plants. 



Christiania, August 6 A. Blytt 



Determination of " H" 



Since the publication of a method for the determination of 

 the value of the horizontal component of the earth's magnetism 

 by Mr. A. Gray in Nature, vol. xxvii. p. 32, I have worked 

 out the value of " H" for my laboratory here, and from six sets 

 of experiments carried out daring the month of March in a 

 small building constructed free from iron near the laboratory, I 

 find " H" to equal o 1S365. The method proposed by Mr. 

 Gray was closely adhered to throughout the experiments. 



Taunton, August 8 Frederic John Smith 



Fireball 



About 8.25 p.m. on the Ilthinst. my attention was suddenly 

 attracted in the direction of ihe window of my dining-room, 

 which looks south, by a brilliant ball of fire of a deep amethyst 

 colour. It was travelling across the clear blue ,-ky at the rate of 

 about twenty miles an hour in an eisterly direction and at an angle 

 of 45°. Before disappearing behind a cloud it seemed to throw 

 a few particles of itself forwards at a greater speed than that at 

 which it was travelling. I trust others ;aw it under more 

 favourable circumstances, and that they will communicate their 

 experience of its course to you. Charles F. Casella 



The Lawns, Highgate, August 14 



Palaeolithic Implements at Stratford 



Allow me to say that a few weeks ago I found an abraded 

 ochreous oval Palceolithic implement at Stratford (in situ two 

 feet from .-urfacr). 1 have shown it to Mr. W. G. Smith, who 

 says it is very interesting, as implements are rare in that locality, 

 and especially ova] ones, and he thought it as well for me to 

 communicate with you, as it may interest some of your readers. 



49, Beech Street, E.C. G. F. Lawrence 



EARTH PULSATIONS 



FOR many years philosophers have speculated as to 

 whether the surface of the earth is really so stable 

 as it usually appears. With the sudden and violent 

 motions of our soil which we call earthquakes man has 

 been familiar since the earliest times, and the origin of 

 these disturbances has always formed a fruitful source 

 of speculation. With the help of properly constructed 

 instruments, our knowledge of the nature of these move- 

 ments has during the last few years been greatly extended, 

 and we are brought to the conclusion that these natural 

 vibrations are propagated through the surface of our 

 earth in a manner very different to that which we 

 should have anticipated from our knowledge of elastic 

 solids. Another order of earth movements which, in the 

 hands of Timoteo Bertelli of Florence, M. S. di Rossi of 

 Rome, and other Italian investigators, have recently 

 received considerable attention, are Earth Tremors. 

 From observations carried on during the past ten years 

 it would appear that the soil of Italy is practically in a 

 perpetual state of vibration, even in districts far removed 

 from volcanic centres. On account of the smallness in 

 the amplitude of thtse motions they are only to be 

 observed with the aid of specially constructed instru- 

 ments. Messrs. George and Horace Darwin, in connec- 

 tion with their experiments on the disturbance of gravity 

 caused by lunar attraction, have shown that these move- 

 ments are common to the soil of Britain. Like observa- 



tions have been made in Japan, and it does not seem 

 improbable that after further experiments have been 

 carried out we shall be brought to the conclusion that the 

 surface of the whole globe is affected with similar micro- 

 seismical disturbances. 



In addition to these minute movements, which escape 

 the attention of the ordinary observer on account of the 

 smallness of their amplitude, theoretical investigation has 

 shown that there may be existing in the soil on which we 

 live movements which have escaped our attention on 

 account of the slowness of their period. These motions 

 for want of a better term I call Earth Pulsations. Mr. 

 George Darwin in his last report to the British Associa- 

 tion has shown that movements of that nature may be 

 produced by barometrical variation. A rise of the baro- 

 meter over an area is equivalent to loading that area with 

 a weight, in consequence of which it is depressed. When 

 the barometer falls, the load is removed from the area, 

 which in virtue of its elasticity rises to its original posi- 

 tion. This fall and rise of the ground completes a single 

 pulsation. 



On the assumption that the earth is extremely rigid, 

 Mr. Darwin calculates that if the barometer rises an inch 

 over an area like Australia, the load is sufficient to sink 

 that continent two or three inches. 



The tides which twice a day load our shores cause the 

 land to rise and fall in a similar manner. (Jn the shores 

 of the Atlantic, Mr. Darwin has calculated that this rise 

 and fall of the land may be as much as five inches. By 

 these risings and fallings of the land the inclination of 

 the surface is so altered that the stile of a plummet sus- 

 pended from a rigid support ought not always to hang 

 over the same spot. There would be a deflection of the 

 vertical. 



In short, calculation respecting the effects of loads of 

 various descriptions which we know are by natural opera- 

 tions continually being placed upon and removed from 

 the surface of various areas of the earth's surface, indicate 

 that slow pulsatory movements of the earth's surface must 

 be taking place, causing variations in inclination of one 

 portion of the earth's crust relatively to another. That 

 pulsatory motions of this description have repeatedly been 

 observed it may be shown that there is but little doubt. 

 The magnitude of these disturbances however is so great 

 that we can hardly attribute their origin solely to the 

 causes which have just been indicated. Rather than 

 seeking an explanation from agencies exogenous to our 

 earth we might perhaps with advantage appeal to the 

 endogenous phenomena of our planet. When the baro- 

 meter falls, which we have shown corresponds to an 

 upward motion of the earth's crust, we know from the 

 results of experiment that microseismic motions are par- 

 ticularly noticeable. 



As a pictorial illustration of what this really means, v.e 

 may imagine ourselves to be residing on the loosely fitting 

 lid of a large cauldron, the relief of the external pressure 

 over which increases the activity of its internal ebullition ; 

 the jars attendant on this ebullition are gradually propa- 

 gated from their endogenous source to the exterior of our 

 planet. This travelling outwards would take place much 

 in the same way that the vibrations consequent to the 

 rattle and jar of a large factory slowly spread themselves 

 farther and farther from the point where they were 

 produced. 



Admitting an action of this description to take place, it 

 would then follow that this extra liberation of gaseous 

 material beneath the earth's crust would result in an in- 

 creased upward pressure from within, and a tendency on 

 the part of the earth's crust to elevation. If we accept 

 this as an explanation of the increased activity of a tremor 

 indicator, then such an instrument may be regarded as a 

 barometer, measuring by its motions the variations in the 

 internal pressure of our planet. 



The relief of external pressure and the increase of the 



