Lovering and Bond on Magnetic Observations at Cambridge. 39 
be considered that in the instance of magnetism the limits are esti- 
mated for nine months while those of the thermometer extend over 
only seven months. The longer period affords of course a wider 
field for the display of extreme cases. The disadvantage to 
magnetism is increased by the influence which the remarkable 
fluctuations of magnetic influence exert upon the regular periodic 
phases. As observations on temperature are hereafter to be 
made parallel with those of magnetic declination we shall be able, 
at some future time, to present the results of a larger and more 
satisfactory comparison of the two sets of changes than our present 
materials can afford. The limits for the times of maximum decli- 
nation and temperature are the same; the limits of minimum de- 
clination are greater than those of minimum temperature. The con- 
siderations which have led to the exclusion of some of the observa- 
tions must now be stated. First, we consider the mean thermometric 
curve for December. The maximum which falls 36 minutes after 
noon is earlier than usual; while the minimum is 12 hours from the 
average time of greatest cold and would come at 6° 26’ P. M. in- 
stead of the morning. We suppose therefore the true time of 
maximum for this month to be merged under irregular changes so as 
to escape notice even in the mean result. This mean was derived 
from three days’ observations. The minimum for one of the days 
happened at 5" 56’ A. M.; for another at 2" 14’ while on the third day 
the changes of temperature were so frequent and disorderly from 
alterations in the wind and sudden variations from a clear to an 
overcast sky that the lowest temperature is at 6" 14 P. M. and the 
highest at 6" 56 A. M. The eccentricities of this day are sufficient 
to vitiate the whole result and prevent the real time of minimum 
from appearing even in the mean of several days. To guard against 
this source of error it is important that the monthly means should 
