1H2 REPORT— 1895. 



zontal displacement, and its amount has varied l^etween one and three 

 minutes of arc. The original instrument has unfortunately been destroyed 

 by fire. 



6. Work at the Central Observatory under the Directorship of K. 

 Kohai/ashi, Esq. — Athough records from the 9G8 outside oljserving sta- 

 tions have accumulated at a quicker rate than that at which they can be 

 tabulated for analysis, many important imiJrovements have been made in 

 the working of the central station. In one room all instruments intended 

 for country stations are tested. These instruments are simplified types 

 of the Gray-Milne seismograph. One test is for the time-recording 

 clocks, another for the clock driving the recording surface, and a third for 

 the multiplication of the horizontal and vertical seismographs. Although 

 several types of spring clocks have been tested, their rates are far from 

 being satisfactory. Cheap pendulum clocks give good rates, but they are 

 generally disturbed at the time of an earthquake. In another room an 

 exceedingly large seismograph, without multiplication, is arranged to 

 record severe motions. In a third room, which is alive with the ticking 

 of clocks and chronometers whicli ai'e at stated intervals compared with 

 time signals fi-om the Astronomical Observatory, there are four seismo- 

 graphs and various types of contact makers. A glass disc recording sur- 

 face, on which the pointers for vertical and horizontal motion rest, is 

 continuously in motion. The recording surfaces of the other instruments 

 are set in motion by the contact makers, after which time intervals are 

 marked upon them from a break circuit chronometer. Mr. N. Outska, 

 who is in charge of this department, finds that for horizontal and vertical 

 contact makers having equal multiplication the former almost invariably 

 closes its circuit before the latter. 



J5 



APPENDIX. 



On Causes prodncinf/ Movements whicli, may be mistaken for Earth 



Tremors. 



The following note refers to observations and experiments made at a 

 small observing .station which has recently been established at Shide, in 

 the Isle of Wight. I reached Shide on July 30, aiid on the following 

 day a pit was e.vcavated in a dry stable, about 3 ft. G in. in depth, down 

 to the upper surface of the disintegrated chalk. 



On August 6 and 7 a brick pier, 6 feet in height and 1 ft. G in. 

 square, was built on a concrete bed to rise freely in the pit. The necessary 

 wooden covering for this was completed at noon on the 16th, and that 

 evening an extremely light horizontal pendulum like R was installed and 

 set to work. This instrument, which I call T, gave a beautifully defined 

 two-line diagram until the 21st, when the clock ceased to drive the film, 

 which had become damp and sticky. This was clearly due to moisture 

 from the drying column being confined in the casing which covered its 

 upper part and the instrument. To overcome the difficulty I placed 

 inside the case two trays, each aliout 6 in. by 3 in., of calcium chloride. 

 Immediately after this tlie pendulum commenced to swing, its range 



