TERRESTRIAL MAGNETISM. 29 
It is to be specially noted that the period of vibration of the 
needle of an instrument should not be twenty seconds, or any aliquot 
part thereof. 
5, List of Term Days and Howrs.—All observations of the inter- 
national co-operation shall be made according to Greenwich Mean 
Time. 
Term days. Observations hourly * Term hours. Observations 
from 0h. p.m. to 0h. p.m. extended during the hour. 
1902. February 1 .. .. .. Oh pm. till 1h. p.m. 
To. «2s os LThepm. ,, 2h. pam: 
March lo. . 0. 6 2hpm , 3h. pm. 
Hb . . . Bhpm , 4h. p.m. 
April 1lo« « ws 4hopm. 4, 5h, pm, 
1) se se ae Sb. pam 4. Gch. pm: 
May i, 6hopm. , 7h. pm. 
15 Thpm. , 8h. p.m. 
June 1 Shpm. , 9h. pm. 
15 9h. pm. ,, 10h. p.m. 
July 1. 10h.pm. ,, 11h. p.m. 
15 .llhpm , Ob am. 
August IL Oham. , lh am. 
wb. lham. ,, 2h. am. 
SeptemberlL .. .. .«. 2ham , 3h. am. 
15 38ham. , 4h. am. 
October 1 4h.am. , 5h. am. 
15 5bham. , 6b. am. 
November 1 6hoam. , 7h. am. 
TS we ae ae TV Rai, 4. Sibi am, 
December 1 .... .. Sham , 9h am. 
15 » O9bam. . 10h. am. 
1903. January 1 - Wham. ,, 11h. am. 
15 -llham , Ob pm. 
February 1 « ee OL pm, .., J he pm. 
Wo. «= « Tipm: 5 2h.pm. 
The variation instruments should be placed in position and fully 
tested as long as possible before February 1, 1902, so that the follow- 
ing terminal observations may be made in January :— 
1902. January 1... .. .. 10h am. till 11h. am. 
5 wk ae ee Dh arm , Ob. pm. 
6. Special Observations on the Term Days.—It is desired that special 
attention be devoted on the term days to observations of atmospheric 
electricity and appearances of the aurora. 
7. The Variation Instruments.—For polar stations it is sufficient 
if the instruments are of such sensitiveness that one scale division, 
equal to one mm. of the ordinates of the curves, correspond to 
For Declination .. .. «. ..  «. Smin. of are, 
Horizontal force .. www. we 10 = 0°00010 C.GS. 
Vertical force ..  .. w. ee we) 10 y = 0°00010 C.GS. 
