290 iScieiitific Intelligence. 



to be of great supplemental value, since the best seismographs 

 give records which are in consequence at different distances from 

 the origin. 



Ill regard to periods and amplitudes : many periods are present 

 during the first and second preliminary tremors and the instru- 

 ments single out and make prominent those which are near the 

 period of the instrument. The periods of the first tremors are 

 mostly limited to a quarter of a minute, of the second tremors 

 mostly between a quarter and a half of a minute. The ampli- 

 tudes of the first tremors range about one-tenth those of the sec- 

 ond. They are measured on the average by tenths and hundredths 

 of a millimeter respectively at distances between 20° and 100° from 

 the origin. The periods of vibration of the regular waves were in 

 general not very far from 30 seconds. In the megaseismic region 

 the amplitudes were oO""™ or more ; at distances of 30° to 50° 

 they have diminished to about 5™™, and we must go as far as 

 100° or so to find amplitudes less than l™". We see, therefore, 

 that the great world-shaking earthquakes cause movements of the 

 earth at great distances which are by no means inconsiderable, 

 and the only reason why they are not felt is that the period, and, 

 therefore, the movement is too slow to make them evident to 

 our senses. In conclusion, Reid points out the importance of 

 damped instruments, of a high magnifying power and an open 

 time scale. It is from instruments possessing these qualities that 

 future increases in this branch of knowledge are to be expected. 



The third part, on the theory of the seismograph, although 

 of great importance is of more particular interest to specialists in 

 earthquake phenomena. j. b. 



2. West Virginia Geological Survey. County Reports and 

 Maps. Pleasants, Wood, and Ritchie Counties' by G. P. Grims- 

 LEY. Pp. xiv, 352, with 21 plates, 16 figures, and 3 maps in atlas. 

 Also, 3Iap of West Virginia (as a separate publication), scale 1 

 miles to the inch, showing coal, oil, gas, and limestone areas, by 

 I. C. White. Morgan town, West Virginia, 1910. — This report 

 by Professor Grimsley gives very complete information regard- 

 ing the three counties named and is of practical as well as 

 scientific value. The chief resources of the i-egion lie in its soils 

 derived from the Permian shales and sandstones and in the 

 abundant accumulations of petroleum. j. b. 



3. Supplementary Investigation in 1909 of the Figure of the 

 Earth and Isostasy ; by John F. Hatford, Inspector of Geo- 

 detic Work, and Chief, Computing Division, Coast and Geodetic 

 Survey. Pp. 80, 5 maps in pocket. Washington, 1910. — The 

 noteworthy contribution by this author on " the Figure of the 

 Earth and Isostasy " has been reviewed in the number of this 

 Journal for February, 1910. The first paper embraced the results 

 of observations up to 1906. In this supplement, the results are 

 confirmed and made more accurate, embracing observations up 

 to 1909 and including some improvements in method. The 

 number of asti'onomical determinations employed in the first 



