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NATURE 



\_Feb. 7, 1889 



motion in their relation to the time. The account that is 

 given of the labours of Italian observers in the field of 

 microseismometry is meagre and unsatisfactory, and the 

 work of M. d'Abbadie and the Darwins in this connection 

 is not so much as alluded to. 



The only part of M. Fouqud's book which can be said 

 to make any addition to existing knowledge is that which 

 deals with the experiments conducted by the author and 

 M. Michel Ldvy on the speed of propagation of artificial 

 disturbances through the earth's crust. In the first instance 

 their method was the same as that used by' Mallet and 

 by Abbot ; the seismoscope was a basin of mercury, in 

 which the observer detected the arrival of the shock by 

 watching in a telescope for the disturbance of the reflected 

 light. In a second series of experiments, the personal 

 equation of the observer was got rid of by causing a 

 convergent pencil of light reflected from the basin to fall 

 on a revolving photographic plate. The light was inter- 

 cepted by a shutter which opened, through electric 

 connection with a seismoscope at the origin of the shock, 

 when the blow was given which caused the disturbance 

 to be propagated. Then, until the arrival of the earth 

 waves blurred the image, a sharply defined circular arc 

 was photographed on the plate, the length of this arc 

 serving to measure the time of transit of the waves. In 

 other instances, where the explosion of dynamite formed 

 the source of disturbance, the explosion was produced by 

 an electric discharge which was made to photograph 

 itself on the plate, thus registering the instant at which 

 the disturbance originated more sharply than by the 

 method of the shutter. Besides observations on the 

 surface of the ground in various localities, and with 

 Tarious qualities of vibrating medium, some^were made 

 entirely underground. The author and his colleague 

 made use for this last purpose of a mine at Commentry, 

 by causing the explosion to take place in one gallery 

 470 feet below the surface, while the seismoscope was 

 set first on the surface of the ground and then in a second 

 gallery 280 feet below the other. As a general result, it 

 was noticed in all cases that the first thing to reach the 

 seismoscope was a, series of very small vibrations, which 

 preceded the arrival of the principal shock. In surface 

 propagation this principal shock was not unique : it was 

 followed by several others, although the initial disturbance 

 at the distant source had consisted in a single blow. 



Notwithstanding the care and pains which have evidently 

 ■been bestowed on the author's experiments, the results, as 

 regards speed of propagation of seismic waves, seem to 

 be subject to some uncertainty. The intervals of time 

 actually measured were too small, and what may be 

 -called the personal equation of the apparatus was too 

 large. The whole amount by which the record lagged 

 through inertia of the apparatus and other causes is esti- 

 mated to be 0301 seconds. Taking one set of experiments 

 (at Creuzot), the recorded time-interval, when the seismo- 

 scope was 490 metres from the source, was o 105 seconds ; 

 but to this small quantity we have to add the above large 

 error of o"3oi seconds before deducing the velocity. It 

 should be added, however, that observations made at a 

 more distant station gave results according well with the 

 velocity so deduced. The velocities ranged from about 

 3000 metres per second in granite to 300 metres per 

 second in sand. The results as to rocky soils are of the 



same order of magnitude with those of Abbot, and with 

 the velocities which have been inferred from laboratory 

 experiments on the density and elasticity of rocks. The 

 figures given refer to the rate of propagation of the group 

 of waves, as measured by the arrival of the first sensible 

 motions — the motions, namely, which form the advancing 

 edge of the group. But the group widens as it travels, 

 and a much smaller speed would be deduced by reference 

 to the passage of the principal wave or waves. 



The first and main part of M. Fouqud's book, entitled 

 " A General Study of Earthquakes," concludes with an 

 interesting detailed account of these experiments. The 

 second part will appeal to a wider circle of readers. It 

 is a narrative of the principal earthquakes which have 

 been felt from 1854 to 1887, including those of San Sal- 

 vador in 1854, 1873, and 1879 ; of Simoda, in Japan, in 

 1854 ; of Ischia in 1883 ; of Andalusia in 1884 ; and of 

 the Riviera in 1887. The account is pleasantly written, 

 and is embellished by a number of photo-engravings 

 showing the mischief wrought by these destructive shocks. 



PERIPA TUS. 

 Studies from the Morphological Laboratory in the Univer- 

 sity of Cambridge. Vol. IV.— Part I. A Monograph of 

 the Development of Peripatics ciipensis. Part 2. A 

 Monograph of the Species and Distribution of the 

 Genus Peripatus. By Adam Sedgwick, M.A., F.R.S. 

 (London: 1888.) 

 T N these two numbers the editor has reprinted the five 

 papers from his pen on Peripatus, which have 

 appeared in the Quarterly Journal of Microscopical 

 Science between 1885 and 1888. From the patient 

 detail with which he has followed the developmental 

 changes, and from the power of generalization from ob- 

 servation which he displays, this research may well be 

 regarded as a model for those who are beginning embryo- 

 logical study. Memoirs such as these, on the other hand, 

 are rarely distinguished for clearness of expression and 

 lucid phrasing, and the one before us forms unfortunately 

 no exception to the generality. 



Since the observations of Moseley and Balfour, it has 

 been anticipated that several difficult morphological prob- 

 lems presented by the Arthropoda would receive their 

 solution from a study of the ontogeny of Peripatus, and in 

 Mr. Sedgwick's hands this hope has been largely realized. 

 The only other recent workers in this field. Miss Sheldon, 

 Mr. Sclater, and Dr. von Kennel, have studied forms 

 from New Zealand and the West Indies ; and while the 

 observations of the latter are in many points at vari- 

 ance with those before us, some of the disagreement is 

 undoubtedly due to the different development of the 

 different species. Like most of such primitive types, 

 the species of Peripatus are widely and discontinuou-sly 

 scattered, and exhibit considerable structural and em- 

 bryological discrepancy. Such a discrepancy occurs 

 at the outset. The ovum of the New Zealand form 

 is large, and consists mainly of deutoplasm ; that of 

 the Cape species, the subject of the present memoir, is 

 smaller, and, while now actually devoid of yolk, forms a 

 loose reticulum of protoplasm which appears to imply its 

 former presence between the meshes: in both of these 



