144 



hYlM.it of Magnetical Observations at Falmouth Observatory 

 for the Year 1898. Latitude 50 9' 0".N., Longitude 

 5 4' 35" W. ; heiglit, 167 feet above mean sea-level. 



The Declination and the Horizontal and Vertical Forces are deduced 

 from hourly readings of the photographic curves, and so are corrected 

 for the diurnal variation. 



The results in the following tables, Nos. I, II, III, IV, are deduced 

 from the magnetograph curves which have been standardised by 

 observations of deflection and vibration. These were made with the 

 Collimator Magnet, marked 66A, and the Declinometer Magnet, marked 

 66c, in the Unifilar Magnetometer No. 66, by Elliott Brothers, of 

 London. The temperature correction (which is probably very small) 

 has not been applied. 



In Tables V and VI the Vertical Force values, also deduced from 

 the Photographic Curves, have been standardised by observations of 

 Dip and of Horizontal Force, and are published for the first time. 

 The January results are based on four days' means, and the June and 

 Octoter results on the means of three days only. No temperature 

 correction has been applied, and this probably has modified to some 

 extent the apparent law of variation of the Vertical Force throughout 

 the twenty-four hours. As is not unusual with a new instrument, some 

 discontinuities occurred in the course of the year. 



In Table VII, H is the mean of the absolute values observed during 

 the month (generally three in number), uncorrected for diurnal varia- 

 tions and for any disturbance. V is the mean of the products of the 

 tangent of Dip and H. 



In Table VIII the Inclination is the mean of the absolute observations, 

 the mean time of which is 3 P.M. The Inclination was observed with 

 the Inclinometer No. 86, by Dover, of Charlton, Kent, and needles 1 

 and 2, which are 3 inches in length. 



The Declination and the Horizontal and Vertical Force values given 

 in Tables I to VI are prepared in accordance with the suggestions made 

 in the Fifth Report of the Committee of the British Association on 

 comparing and reducing magnetic observations^ and the time given is 

 Green wich Mean Time, which is 20 minutes 18 seconds earlier than 

 local time. 



The following is a list of the days during the year 1898 which were 

 selected by the Astronomer Royal as suitable for the determination of 

 the magnetic diurnal variations, and which have been employed in the 

 preparation of the magnetic tables : 



