







5 Vibrations. 



m. 



7 



330 



m. 



9 



350 



2 20 



7 



560 



10 



00 



2 40 



8 



22-0 



10 



250 



2 3-0 



8 



47-5 



10 



49-5 



2 2-0 



9 



10-5 



11 



14 



2 3-5 



Inteoduction. xxix 



August 22^ 20^. There being a considerable natural vibration of the bifilar 

 magnet, with little or no change of mean position, the following estimations were 

 made at the extremities of the arcs. 



Mean. 



2"! 2s-9 



Mean, 1 vibration = 24s-58. 



The arc of vibration was 11' during the first 9 vibrations, 9' at the 10th, and at the 

 end of the 11th the magnet stopped. 



Oct. 8*^ ^. The magnet vibrated by a knife. 



2 estimations, mean of 4 vibrations, 1 vibration 25^-22 

 2 ... ... 4 ... 1 ... 26=-28 



8 estimations, as below. 



78^-17 



^ 





3 Vibrations. 



16-2 



350 



78-8 



42-8 



0-5 



77-7 



8-8 



270 



78-2 



350 



53-0 



78-0 





1 vibration = 



26=06. 



Oct. W 23*^. Natural vibration. 





2 estimations, mean of 11 vibrations, 1 vibration 25s-18. 



25= was used throughout in the observations. 



32. The point of the scale coinciding with the vertical wire of the fixed tele- 

 scope is estimated to a tenth of a division, at 25^ before the minute of observation, 

 at the minute, and 25' after it ; the mean is deduced, as in the declination, from the 



formula - — j — ^, a, 6, and c being the three readings. 



The mean thus obtained is corrected to the temperature of 26° Fahr., this 

 being below the lowest temperature which has occurred within the observatory. A 

 constant quantity of 300 '0 has been added to all the readings, in order that the 

 mean readings might be about 500 ; in this case the greatest changes will be con- 

 tained within and 1000. 



The values of 1 scale-division, in parts of the whole horizontal force, are given 

 beneath ; they are also given at the foot of each page of the Daily Observations of 

 Magnetometers. 



Tables have been formed giving the temperature-correction for every tenth of 

 a degree Fahr. to a tenth of a scale-division, from the formula 



MAG. AND MET. OBS. VOL. I. h, 



