Report on the Observatory Department. 



423 



employed, and by removing the sulphuric acid at regular periods — 

 generally fourteen or fifteen days — the troubles previously experienced 

 with the " setting " of the needle and with the shift of zero has been 

 largely overcome. 



No systematic use has been made of the thirty-six Clark cells men- 

 tioned in the 1898 Keport, but they have been employed to check the 

 scale values of the two portable electrometers. 



Scale-value determinations of the electrograph were made on April 2, 

 July 14, and October 25, and the potential of the battery has been 

 tested weekly. Forty cells only have been employed during the year, 

 giving about 30 volts. 



With a view to promoting uniformity in procedure, the Superin- 

 tendent, at the suggestion of the Meteorological Office, had an inter- 

 view with Mr. C. T. K. Wilson, F.K.S., and Mr. W. Nash, of Greenwich 

 Observatory, who were shown the electrograph arrangements and the 

 means adopted for standardising the curves. The stoppage this 

 entailed in the working of the instrument was utilised in giving it a 

 thorough cleaning. A new bifilar suspension was also fitted to the 

 needle, and the wire leading from the can to the electrometer was 

 bedded in paraffin wax in hopes of improving the insulation. 



Inspections. — In compliance with the request of the Meteorological 

 Council, the following Observatories and Anemograph Stations have 

 been visited and inspected : — Xorth Shields, Glasgow, Aberdeen, 

 Alnwick Castle, Deerness (Orkne}^), Falmouth, and Fort William, by 

 Mr. Baker; and Radcliffe Observatory (Oxford), Stonyhurst, Fleet- 

 wood, Armagh, Dublin, Valencia, and Yarmouth, by Mr. Constable. 



III. Seismological Observations. 



Professor Milne's " unfelt tremor " pattern of seismograph hai? been 

 maintained in regular operation throughout the year; particulars of 

 the time of occurrence and the amplitude in seconds of arc of the 

 largest movements are given in Table I, Appendix III. 



The " disturbance " on January 20 was particularly noticeable. 



The movement was the largest that has yet been fully recorded at 

 the Observatory, the maximum amplitude being 15 mm., or 12 6 seconds 

 of arc. The next largest disturbance was on October 29, with a maxi- 

 mum of 12 mm., or 9*5 seconds of arc. 



The action of the boom was not altogether satisfactory during 

 August and September, and on September 27 the old boom was 

 replaced by a new one of standard pattern. The balance weights are 

 at 117 mm. and the tie at 127 mm. from the cup end of the boom. 



The point of the bearing pivot on the stand was also improved. 



A detailed list of the movements recorded from January 1 to 

 December 31, 1900, was made and sent to Professor Milne, and will 

 be found in the 'Report' of the British Association for 1901, " Seismo- 

 logical Investigations Committee's Report." 



