50 Lovering and Bond on Magnetic Observations at Cambridge. 
when strange fluctuations of greater or less amount are not exhib- 
ited; but there are some periods distinguished above all others 
by their remarkable frequency and magnitude. We annex a brief 
history of each month in this respect. 
1840. 
March 27-8. No perturbations of importance ; only two unusual 
excursions, one at 2" 45’, A. M. Gott. M. T. (March 28) and the 
other at 4" 15’, A. M. 
April. The observations of this month are very defective. 
May 29-30. Term-day. Irregular disturbances of large amount, 
from 11 o’clock, P. M. Gott. M. T.(May 29) to 12" of May 30. The 
whole sweep of the instrument through the day is 57',2; and once, 
between 3" 50’ A. M. and 4" 10’ the declination changes 47’, 2 in 11™ 
or 4 times the average daily swing from maximum to minimum. 
The other days observed in May were not distinguished above 
the average by perturbations, 
June. The ten days observed in this month were all unusually 
quiet. 
July 24-5. Between 6 and 8 o’clock, P. M. Gott. M. T. (July 
25) the are of vibration of the Magnetometer amounted to 20’ so as 
to require the substitution of its extreme limits instead of the 12 
readings at intervals of 10 seconds. But this large movement was 
not accompanied by any considerable change of absolute declination 
and the whole magnetic day was undisturbed. 
August. The Term-day of Aug 28-9 was greatly deranged 
from 10" 40' P. M. Gott. M. T. to 8" A. M.,and small perturbations 
were experienced for 4 or 5 hours after this time. The whole range 
of the magnetic declination amounted to 61. Qnce between 6" 40: 
and 7° 20’ A. M. the change of declination exceeded 43’ in 27 
minutes, The other days observed in August were still. 
