172 Lieut. Foster's observations on the diurnal changes 
March 9,2nd. North end of Needle to the S. 83° W. 
The following summary of the observations at this point, is 
given here, merely to prevent breaking the preceding series : 
they were commenced at 6 o'clock in the morning, at which 
time the north end of the needle was at S. 83° 30' W. where it 
remained until ~ past 9 h ; it then moved to S. 85° W, and 
became nearly stationary until about n h so 1 ”, at which time 
it was at S. 8i° 30' W. and soon after, I observed it vibrating 
rapidly in very small arcs, which were continued with 
different degrees of intensity for the space of a quarter of an 
hour. During this time, simultaneous observations on the 
times of vibration of a horizontal needle were made, and as 
great fluctuations were observed in the intervals of 10 vibra- 
tions, I have inserted them in detail, as follows, in order to 
show the variations of horizontal intensity which take place 
in short intervals, and to which must be attributed the 
irregular vibratory motion observed in this needle. 
Mean Time of 
Observation, 
Intervals of 
10 vibrat. 
Remarks. 
h. m. s, 
II 38 5,2 
41 IO 
44 i 3 
47 ! 6,5 
50 19 
S 3 20,7 
56 22,5 
m. s. 
3 4.8 
3 3 
3 3>5 
3 2,5 
3 n7 
3 
It appears by these observations, that 
the intervals of 10 vibrations, exhibit 
changes of horizontal intensity to the 
amount of -^th part of those intervals, 
in the space of quarter of an hour. 
