Earthquake Experiments in Japan. 357 



vessel of the size or shape which will ensure a washing-up at all. 

 A vessel, the fundamental period of oscillation of the liquid in 

 which nearly coincides with the period of the earthquake, 

 would possibly show a considerable motion. A difficulty here 

 arises however. Our observations show that few earthquakes 

 have any definite period ; and different earthquakes have 

 generally different, sometimes very different, periods. 



(b) Columns. — These generally consisted of round cylinders, 

 with their ends cut very accurately at right angles to the axis 

 of the cylinder. Specimens of such cylinders, of various dia- 

 meters and the same height, were set on end on a level plane 

 with the view of finding, from the direction in which they fell, 

 the direction of motion during the earthquake-shock. We 

 were somewhat surprised to find that even the smallest cylin- 

 der that can be set on end but seldom falls in ordinary non- 

 destructive shocks. When the shock is tolerably severe, they 

 fall in various directions, even when placed on the same 

 slab. The reason of this appears to be that most earthquakes 

 commence gently, — the columns rock, and, whilst rocking, 

 gradually change their plane of motion before being over- 

 turned. Occasionally it may be due to the presence of two 

 sets of vibrations in different directions, some columns being 

 overturned by one set, whilst others are overturned by the 

 other set. Because of this indeflniteness in the indications of 

 columns, we have called them Seismoscopes. In addition to 

 round cylinders, columns of various shapes (as, for instance, 

 inverted cones) have been employed. Columns have also 

 been caused to stand on segments of small spheres. These 

 variations have not as yet shown any advantage over the ordi- 

 nary column. 



Besides the ordinary columns which are used as earthquake- 

 indicators, we may mention bodies like strips of glass, pins, 

 &c, which will not stand unless supported on one side. When 

 such bodies are thus supported, they are overturned more 

 readily by motions inclined to the plane of support than the 

 finest columns we are able to set on end. In employing this 

 principle of propping up, it is necessary to use a number of 

 bodies placed against planes in different azimuths. 



(c) Microphones, or circuit-breakers in conjunction with a 

 galvanometer so arranged that if the needle swings it comes 

 into contact with a piece of iron and is held, and many other 

 similar contrivances have been employed to indicate small 

 motions. 



(d) Tremor-Indicator. — This is a modification of a pendu- 

 lum seismometer, in which the bob of the pendulum is at the 

 time of an earthquake approximately steady. Against this 

 bob are placed the ends of two small strips of wood resting in 



Phil. Mag. S. 5. Vol. 12. No. 76. Nov. 1881. 2 E 



