TRANSACTIONS OF SBCTION C. 647 



Several very sensitive forms of seismoscopes were described, such as tlie 

 ' tremor indicator ' and ' circuit-closer seismoscope,' fidl descriptions of -which will 

 shortly appear in the 'Transactions' of ihe Seismological Society of Japan for 1881. 



A large number of different contrivances for the purpose of measuring jvccurately 

 the amplitude, period, and direction of motion at any instant during an earthquake- 

 shock is referred to. For descriptions of such contrivances reference may be 

 made to the * Philosophical Magazine ' for September 1881, and to the ' Transac- 

 tions ' of the Asiatic Society of Japan for 1880-81, in one or other of which 

 accounts of most of them will be found. 



The second part of the paper treats of earthquake motion generally; the 

 different modes of determining theoretically and practicalh' the rates of propaga- 

 tion of an earthquake wave ; the effect of continued action onthe ai-ea afl'ected ; the 

 different modes of determining the origin ; the effects of earthquakes on buildings 

 of different form and in different situations; the proper mode of determining 

 the intensity of an earthquake-shock ; the explanation of the rotation of bodies by 

 earthquakes, &c. 



It is pointed out that earthquake-motion is generally of a very irregular 

 character, that it usually begins gradually, reaches a maximum somewhat suddenly, 

 and afterwards passes through several minima and maxima. The period of vibra- 

 tion of a great number of earthquakes observed by the authors, varied between 

 one-half and one-fifth of a second, while the total time of disturbance varied 

 from one-half to three minutes. Reasons are given for believing that earth- 

 quakes which last for a long time are propagated farther than those which last for 

 a short time, even when the intensity of the latter is the greater. 



With regard to the determination of the origin of sliock, the great value of 

 accurate time-observations is pointed out, and a sketch of several different modes 

 of making such observations is given. 



The eff"ect of an earthquake on a building appears to depend mostly on the 

 nature of its foundation (the best probably being a somewhat broad concrete foun- 

 dation resting on a soft bottom) ; the agreement or non-agreement of the vibrational 

 period of the different parts ; and the situation of the building, it being unsafe to 

 build near the edge of a plateau, or near the junction of a plain with a steep hill 

 or cliff. 



It is pointed out that in estimating the intensity of an earthquake-shock the 

 maximum velocity of a particle on the earth's surface during the shock should be 

 taken, and that the intensity is best measured in terms of the square of this 

 velocity. In other words the intensity is proportional to amplitude of movement, 

 and inversely proportional to square of period. The usual explanation of the 

 rotation of bodies during a shock, namely, that of vortex movement, is referred 

 to, and it is pointed out that this is not likely to produce the rotation in question ; 

 but, on the other hand, that if a direct backward and forward movement be given in 

 proper direction a rotation will take place. For simplicity, the body may be 

 supposed to have a rectangular base. If the direction of the shock is at right 

 angles to one of the sides or along one of the diagonals, no rotation will take place; 

 but if it be inclined to either of these directions, it may be resolved into two com- 

 ponents, one of which tilts the body up in one corner while the other rotates it 

 round that corner as a pivot. The application of this to the determination of 

 direction is referred to. 



3. Final Report on the Thermal Conductivities of certain RocJcs, showing 

 especially the Geological Aspects of the Investigation. — See Reports, 

 p. 126. 



4. On an International Scale of Colours for Oeological Maps. By 

 W. ToPLEY, Oeological Survey of England and Wales. 



The author described the objects of the International Geological Congress, 

 appointed to meet at Bologna in September 1881. Three main subjects to be dis- 



