522 Reviews—Prof. Fouqué on Earthquakes. 
In a recent work on Earthquakes, we should expect to find a fair 
discussion of some of the excellent seismographs which have lately 
been invented in Japan and other places. M. Fouqué excuses him- 
self from the task of writing such a chapter (pp. 7-8), partly on the 
ground that the subject deserves to be treated in a separate work 5 
partly because improvements are continually being made in these 
instruments, and their description will gain by being deferred for 
some years. If this latter principle were consistently carried ove, 
how many works on natural science would ever see the light? But 
the influence of these reasons is not very apparent. For the average 
length of one of M. Fouqué’s chapters is a little less than 18 pages ; 
and the scattered references to seismographs and other instruments 
amount to rather more than 20 pages, excluding the description of 
those used in the experiments on the velocity of earth-waves. Now, 
of these twenty pages, seven are devoted to Cavalleri’s seismoscope — 
and some of the results that have been obtained with it. But, owing 
to the fact that the period of vibration changes during an earthquake, 
and to the natural defects of the instrument itself, these pages are of 
little value. Of other instruments alluded to, the accounts are too 
short and incomplete to be of much use, and in only one case is the 
description accompanied by a figure. It is to be hoped therefore 
that, in a new edition, M. Fouqué will see his way to replacing 
these twenty pages by a chapter in which a few of the more trust- 
worthy seismographs are exactly figured and described. 
In the chapter on the “centre of disturbance,” the approximate 
and imperfect nature of our methods for determining its superficial 
position and depth is carefully pointed out. The method employed 
by Messrs. Dutton and Hayden, in the case of the Charleston 
earthquake, is however quoted with some approval. But this 
method makes the depth of the centre independent of the intensity of 
the initial disturbance. For instance, in every earthquake originat- 
ing at a depth of 34 miles, the intensity would, if the method were 
correct, decrease most rapidly at a distance of about two miles from 
the epicentrum. But we can imagine the intensity of the earth- 
quake to be so feeble initially that it cannot, by the most delicate 
instrument yet constructed, be felt at so great a distance from the 
epicentrum, or perhaps even be felt at the surface at all. The 
method is thus unreliable, however carefully applied. Perhaps a 
more accurate statement of it would be that it gives an inferior 
limit to the depth of the seismic focus. 
Microseismology, one of the latest and most fascinating develop- 
ments of the science, is dismissed in a short chapter of a dozen pages. 
Half of the chapter is allotted to the perturbations of magnetic in- 
struments during earthquakes. But, whilst these interesting pages 
could ill be spared, might we not have expected a fuller account of 
the other advances that have recently been made? Such a chapter 
must surely be incomplete when the names of Bertelli, the founder 
of microseismology, of d’Abbadie, and the Darwins are not so much 
as mentioned. 
The rotation of columns during earthquakes is an interesting 
