74 Report of the Kew Committee. 



Horizontal Force, and Vertical Force variations have been secured 

 uninterruptedly throughout the past year, and in accordance with the 

 usual practice the scale values of all the instruments were determined 

 in January last. 



The following values of the ordinates of the different photographic 

 curves were then found : 



Decimation : 1 inch=0 22'-04. 1 cm.=0 8'7. 



Bifilar, January 12, 1888, for 1 inch H = 0'0279 foot grain unit. 



1cm. = 0-00051 C.G.S. unit. 

 Balance, January 16, 1888 1 inch cV= 0'0282 foot grain unit. 



1 cm. = 0-00051 C.G.S. unit. 



The distance between the dots of light upon the vertical force 

 cylinder having become too small for satisfactory registration, the 

 instrument was re-adjusted for balance. This was done on January 

 19th, after which the scale value was re- determined with the following 

 result : 



Balance, January 21, 1888, for 1 inch V = 0*0278 foot grain unit. 



1cm. = 0-00050 C.G.S. unit. 



In February experiments were undertaken to verify the tempera- 

 ture corrections of the force magnetographs as well as of the 

 barograph by artificially heating the room in which these instru- 

 ments are at work. A rough temporary fireplace was built of bricks 

 and slates, in which a charcoal fire was lighted for several hours. 

 This was subsequently extinguished and the windows were thrown 

 wide open in order to admit the cold night air for a corresponding 

 period. By this means changes of temperature of about 20 F. 

 were several times made. The resultant effect in the case of the 

 bifilar was very small indeed, but with respect to the balance magnet- 

 ometer, it was considerable, as expected. 



In order to ascertain whether the experiments had affected the 

 permanent magnetism of the needles, or had otherwise influenced the 

 instruments, scale value determinations were made on March 20th, 

 and as will be seen by the following note, no appreciable effect had 

 been produced in the sensibility of the V.F. magnetometer by the 

 operation. 



Balance, March 20, 1888, for 1 inch 3V = 0'0277 foot grain unit. 

 1 cm. = 0-00050 C.G.S. 



Small unimportant repairs have been made to the recording 

 apparatus when necessary. 



Although the magnets generally have been more active than in the 

 preceding year, no very large movements have been registered. 



The principal disturbances were recorded on the following dates : 



