354 Mr. T. Gray on an Improved 



right angles to each other, on a band of smoked paper which 

 covered the surface of a cylinder. The cylinder was intended 

 to be kept continuously in motion round its axis by clock- 

 work ; and the recording points were, on the supposition of 

 no motion of the earth, expected to trace continuoasly the 

 same line on the smoked paper in a similar manner to that 

 introduced by Prof. J. A. Ewing, and used by him in his 

 experiments in Japan*. Prof. Ewing used smoked glass for 

 his record-receiving surfaces, and that is a very good arrange- 

 ment when it can be conveniently adopted. It had been pre- 

 viously used by Prof. Milne in apparatus in which the 

 record-receiver was either stationary or automatically started 

 into motion by the earthquake ; and it has since been much 

 used by him and the writer in earthquake investigations. 

 Smoked paper was adopted in the apparatus here referred to, 

 and, when smoked surfaces are used, it is still recommended 

 for the present form, because it is desirable to obtain straight 

 records, written side by side and to the same scale, of all the 

 three components. This, combined with continuous motion, 

 could only be got on a cylindrical surface ; and, considering 

 the risk of breakage, cylinders of glass sufficiently true and 

 inexpensive could not be readily obtained. 



The apparatus used for recording the motions was in prin- 

 ciple the same as that described in this paper, but differed 

 considerably in detail. A separate clock was provided for 

 the purpose of recording the time of occurrence, the record 

 being made on the dial of the clock, which was, at the time 

 of an earthquake, automatically pushed forward into contact 

 with ink-pads fixed to the ends of the hands, a mark being at 

 the same time made on the record-receiver to show at what 

 part of the earthquake the time was recorded. In subsequent 

 instruments this method of recording time was abandoned 

 because, with the improved form of record-receiving appa- 

 ratus, it became unnecessaryf. This will be more particularly 

 referred to when the method of recording time now adopted 

 is being described. 



The instrument above referred to was set up in the Meteo- 

 rological Observatory in Tokio, where it is still in use. Ex- 

 perience with it, however, soon suggested many improvements, 



* See a A new Form of Pendulum Seismograph," Trans. Seis. Soc. 

 Japan, vol. i. part 1, p. 38 \ and " On a New Seismograph," Proc. K. S. 

 no. 210(1881). 



f This refers only to the instruments here described, which are made 

 in this country by White, of Glasgow. In a less complete form of the 

 apparatus made in Japan, and a considerable number of which are in use 

 in different parts of that country, the clock with movable dial is still used. 



