System of Observation, and Personal Establishment. xi 



D, The Declinometer. 



i, Its Reading Telescope. 



A, The Azimuth Circle and Transit. 



H, The Bifilar or Horizontal Force Magnetometer. 



t', Its Reading Telescope, 



P, A Pillar for a Collimator (not used). 

 V, The Balance or Vertical Force Magnetometer. 

 I, The Inclinometer. 



B, The Standard Barometer. 

 W, The Anemometer. 



W, The Wind Vane Dial-Plate. 

 T, The Thermometer Case. 



C, The Mean Time Clock. 

 S, The Copper Stove. 



n s, The Astronomical Meridian. 

 D t, The Magnetical Meridian. 

 The two vanes to the right in the elevation are those for the direction and 

 force of the wind ; the other two were added after 1843. 



§ 2. System of Observation, and Personal Establishment. 



5. The system of observation followed in 1841 and 1842 consisted of four 

 daily observations of the magnetical and meteorological instruments, at the hours 

 of 8 and 11 a.m., and 2 and 5 P.M., hours recommended by Dr Lloyd for one per- 

 manent observer ; * of term observations, made once a month for 24 hours ; of 

 observations of magnetic dip ; and of extra magnetical observations, made during 

 marked magnetic disturbances. The personal establishment in 1841 and 1842 con- 

 sisted of one permanent observer, and three assistants on term-days. It seemed 

 desirable to render the daily observations somewhat more complete ; and as this 

 would also necessarily entail a greater amount of labour in reductions. Sir Thomas 

 Brisbane, on my suggestion, through Professor Forbes, and with his advice, added 

 another permanent observer to the establishment. Mr John Welsh, a student in 

 Arts of the Edinburgh University, was appointed in the end of December 1842. 

 The term-assistants in 1843 were Messrs HoGG and DoDS, who assisted in the pre- 

 vious year. In 1843, the daily observations were made at every even hour of Got- 

 tingen mean time, from 6 a.m. till 10 P.M., or at every two hours, from 5'' 10™ a.m. 

 till 9"^ 10™ P.M., Makerstoun mean time. The other observations consisted of term- 



* The observer had also the charge of a Transit Instrument, and of several Sidereal Clocks, which 

 were compared daily. 



