36 Lovering and Bond on Magnetic Observations at Cambridge. 
perturbations which do not generally begin before 7 or 8 o’clock in 
the evening commenced their operations on this day earlier than usual 
by many hours. We are confirmed in this opinion by examining 
the curve of the next day from 10 o’clock Gott. M. T.* This 
curve is a continuation of the first from the place where it ends 
at the right hand of the Plate; and we see from it that the per- 
turbations continue during the whole night and morning till nearly 
the time of the next minimum; one digression of the Magnetometer 
within 30 minutes about an hour before midnight of October 21st 
amounting to 20’. These agitations are felt at intervals till the fol- 
lowing midnight and may be allowed any influence that is thought 
justly attributable to them in hastening the time of maximum of the 
second day. It is admitted that this maximum appears satisfactori- 
ly formed on the curve so as to leave no doubt that the time se- 
lected for it, 11" 46’ A. M. Cambridge M. T., is correct. And 
further, in regard to the minimum of the last of the five days, there 
may be a question what precise moment between 5 and 7 o’clock 
A. M. Cambridge M. T. should be chosen. It seems proba- 
ble that the minimum should be formed earlier than usual on 
this day as the maximum occurs later than the average time ; 
so that the whole curve from the point of minimum to that of maxi- 
mum takes a wider sweep of time than usual; a glance at the Plate 
makes this clear. These explanatory suggestions as to the extreme 
cases, if valid, will give still greater preéminence to the diurnal 
magnetic curves over the cotemporaneous thermometric curves so 
far as relates to the present comparison. But it is not at all necessa- 
ry for our purpose to press this apology. No abatement for similar 
reasons is required in regard to the thermometric curves. Although 
* The commencement of the Magnetic day is in all cases at 10 o’clock 
P. M. of mean Gottingen Time. 
