266 



NATURE 



\yan. 2 1, 1 886 



In summarising this portion it is stated that "the main 

 axis of disturbance extends on each side of a hne about 

 five miles in length, having a direction north-east and 

 south-west from Wivenhoe to Peldon. Along this axis 

 the greatest intensity was manifested, as shown by the 

 large percentage of dislodged chimneys, dismantled roofs, 

 &c., and more especially by the fracturing of solid 

 masonry." Following this sumniary there are the com- 

 plete records from other parts of Essex and all the other 

 counties over which the disturbance extended. Among 

 the foriiier we notice a very full report from Bocking, 

 furnished by Mr. E. B. Knobel, Sec.R.A.S. It is of 

 interest also to observe how widely the shock was felt 

 over London ; records are given from every quarter of 

 the town, and we can but feel thankful that the " axis 

 of disturbance " was not neirer home, or the destruction 

 to life and property would have been most disastrous. A 

 glance at the map, giving the general distribution of the 

 shock, shows that the vibrations were felt as far off as 

 Altrincham in Cheshire, at Sidbury in Shropshire, Street 

 in Somersetshire, Exeter, the Isle of Wight, and across 

 the Channel at Boulogne and Ostend. 



The next section will be of special interest to geolo- 

 gists. It is headed " The Earthquake in Relation to 

 Geological Structure," and the first portion deals with the 

 effects of the shock upon underground waters. These 

 effects are, briefly, the raising of the water-level in deep 

 wells near the origin, the falling off of the supply to 

 surface wells, and the rendering turbid of the water 

 derived from the Chalk at Canterbury and in surface 

 wells nearer the centre of the disturbance. The records 

 kept by the Underground Water Committee of the 

 British Association have enabled the authors to give a 

 most valuable series of measurements made at Bocking 

 on behalf of this Committee by Mr. D. Radford Sharpe. 



One of the most important practical considerations in 

 connection with earthquake damage is the effect of the 

 subsoil and the position of buildings with respect to the 

 general physical features of the district. This branch of the 

 subject is fully dealt with in the present geological section 

 of the Report, and the authors point out that, owing to 

 the circumstance of the shock having originated beneath 

 a district consisting entirely of London Clay and drift 

 deposits, no very definite conclusions can be drawn as to 

 the efiects of the superficial geology in determining the 

 distribution of the damage. They incline to the view 

 that the damage was increased in some cases by the 

 situation of buildings at the junction of different forma- 

 tions, where, in accordance with well-known dynamical 

 principles, the earth-wave undergoes reflection and re- 

 fraction. A considerable amount of evidence is given to 

 show that both in this and other earthcjuakes there is a 

 tendency for the shock to make itself felt with special 

 distinctness along " free margins, such as coast-lines, 

 river-valleys, and lines of outcrop, because in these cases 

 there is no resistance offered in one direction to the 

 vibrating particles in their outward movements." 



In connection with other geological considerations the 

 authors state that their seismic axis corresponds in direc- 

 tion with the coast-line at this part of Essex, and this 

 fact appears to be in harmony with the theory first put 

 forward by Prof. J. P. O'Reilly. Several pages are de- 

 voted to a critical discussion of the evidence furnished by 



the records from beyond the London Basin, from which 

 it distinctly appears that the shock was spread outwards 

 along the older rocks, owing to the superior "seismic , 

 conductivity " of these beds. 



In speculating upon the cause of the eaithquake the 

 authors display great caution. Having dismissed the 

 view of the shock having been due to volcanic agency 

 they go on to say : — 



"The most feasible explanation, in so far as it is safe 

 to hazard any explanation at all, appears to be that of the 

 sudden rupture of deep-seated rocks under a state of 

 strain, the snap and shock accompanying such a fracture 

 being quite competent to produce the effects observed. 

 The precise formation in which this rupture may have 

 occurred cannot even be conjectured ; but the great 

 extent of the shock, on the one hand, and on the other 

 the absence of any perceptible change of surface-level, 

 appear to point to a tolerably deep-seated origin." 



It is then pointed out as a very significant fact that the 

 axis of the present earthquake corresponds in direction with 

 known faults or other disturbances in the Chalk beneath 

 Essex, Suffolk, and Cambridgeshire, and with that of the 

 well-known Deptford fault. 



In the seventh section there are collected a number of 

 miscellaneous observations which could not well find 

 place in the preceding portions of the Report. Mallet's 

 method of determining the " angle of emergence " by the 

 cracks in buildings has been found useless in the present 

 earthquake, and the authors wisely state : — 



" We have not thought it advisable to give any calcu- 

 lations of the depth of the origin of the disturbance, being 

 convinced that under the present circumstances such 

 determinations would only give a fictitious semblance of 

 certainty to the results." 



A full discussion of the time-records is then given, and 

 the mean velocity of propagation of 9183 feet per second 

 deduced from the most trustworthy. The remainder of 

 this section contains " Observations on Direction," " Per- 

 sonal Experiences of Direction," " Order of Succession 

 of Phenomena," the " Direction as given by Clock- 

 stoppages," and an important sub-section on the twists of 

 chimneys. 



The eighth and last section gives a general summary 

 of the whole work. In a postscript, two observations of 

 considerable interest are recorded, the first being the 

 registration of the shock and subsequent earth-tilt at 

 Leeds by a barograph, and the second the displacement 

 of Mr. C. L. Prince's equatorial at the Crowborough Ob- 

 servatory in Sussex. The volume concludes with a short 

 appendix, which relates to the list of British earthquakes. 



SYSTEMATIC SMALL FARMING 

 Systematic Small Fanning. By Robert Scott Burn. 



(London : Crosby Lockwood and Co., 18S6.) 

 ' j 'HIS volume may be divided into two parts. In the 

 -L first few chapters the author shows, with consider- 

 able clearness, the disadvantages under which small 

 farmers or peasant proprietors are placed. The topic 

 is one which has recently been discussed in connection 

 with legislative projects looming upon the political hori- 

 zon, and Mr. Scott Burn has contributed towards its 

 elucidation. " While he would be glad to see a limited 



