— 2 — 



'Flic dctormiimtion of tin- forci- of pmvity wm a differential one, «ind 

 consisted ij» compnriiig tlie times of n single oscillation of iiirariabic pendu- 

 lums nt the two places, Tokio and Ognsawarnjiraa. The method of deter- 

 mining the times of a single oscillntion wns the same ns that descrilx-d in the 

 Memoir No. 5 and its Appendices, and our equipments wen- the same as those 

 employed in the previous excursion to Naha (Loo Choo) and Kagoshima in 

 1882. A few improvements, however, wea« matle oji tlie former method of 

 working. 



The iron bar which was used for banging the pendulnm in previoiu 

 experiments was found to Ix? slightly flexible. This was detected by attaching 

 n mirror to the end of the bar and sighting the reflcctetl image of a scale, 

 placed nt a distance of three metres from the mirror, with a telescop«'. TTiin 

 bar was tested by Prof. Mendenhall in 1880 with a micrometer and was 

 found to be rigid enough for the pendulum then emplnyed. But this 

 could not bo assumed in the present case, since the pendulums were mon- 

 than ten times heavier. A new bar of iron 54 cm. long with a section of 

 11.5 cm. by 2.5 cm. w.is ca«t. This had three screws, two near the st-ige 

 from which the pendulum liiuig !Ui<l one near tlie other end of the bar. A lead 

 weight of 50 kilog. was phiced over the middle of this bar an<l the level of the 

 stage was adjusted by these screws; this gave sufficient stability and rigijiit)- fxn 

 observed by the reflected im.nge. 



"We made also a wocxien case for protecting the pendulum from air 

 currents consequent on approach of the observer. This case was 30 cm. by 

 27 cm. in section and 148 cm. in length, and it had four glass windows for 

 observing the level of the peTidulum stage, temperature and arcs of oscillation. 

 A small trap-door was made near the bottom of the case on one side. In mani- 

 pulating the break circuit arrangement for giving automatic signals, the 

 observer put bis b.-uid througb Xhh diwr. 



PKNDrLT'MS. 



Three pendulums were employetl called H, C, K, for convenience. It 

 may be remarked that A and D were sent to America for comparing the determi- 

 nation of the force (>f gravity here with that there. H and C were the which ones 

 taken to Naba aj;d Kagoshima iji 1882. K was a new one, which differed 

 from the others by having the knife-edge at the upper end in the form of a 

 T-square instead of a crOss. This pendulum fitted the agate jilajie stage which 

 was made by Salleron of Paris and was used in making absolute determinations 

 in 1880. Thestage, with its four leveling sca-ws, was moiuited on the iron bar 

 already mentioned. Two of the screws rested in V-shaped grooves cut in the 

 bar, and tjie other two on the plane surface of the bar ; while the stage as a whole 

 was fixed to the same by a couple of brass clamps. 



