Lovering and Bond on Magnetic Observations at Cambridge. 35 
greatest and least temperature; and yet the last phenomena, as 
every one believes, depend on the apparent daily motion of the sun. 
It is to be observed that these days were selected and the curves 
published before the comparison was made. They are to be re- 
garded as a fair index of the whole series of observations of a simi- 
lar character taken in each month since August, 1840, inclusive 
when the thermometric and magnetic changes were first observed in 
connexion. As far as any dependence can be placed upon them, 
they authorize us in stating that the diurnal magnetic curve is a 
more exact and definite function of solar time than the regular daily 
change of temperature. In whatever particular the comparison is 
made the preference attaches to the magnetic curves. We have 
seen how it is in regard to the limits of the time of maximum and 
minimum. The greatest variation of any daily range of the ther- 
mometer from the mean of the ranges is more than +3 of the mean 
range. The greatest variation of any magnetic range from the mean 
of the magnetic ranges is less than + of the mean of the magnetic 
ranges. ‘The most observable deviations from mean results in the 
magnetic observations pertain to the times of maximum declination 
of October 21-2 and 22~—3 and the times of minimum declination 
of October 25-6. If they were excluded, the limits of the times of 
maximum declination would be reduced from 3 hours to 1 hour and 
10 minutes and of minimum declination from 4 hours to 1" 5’. 
In regard to the first of these days, an unusual and irregular de- 
rangement of the magnetic equilibrium occurs between 1" and 3° 
P. M. Cambridge M. T.; and there is reason to think that 
the maximum declination, if the extraordinary influence could be 
eliminated, would fall between these disturbed hours. There is 
even a doubt whether now the western excursion at 3 P. M. ought 
not to be taken as the western limit of that day. The irregular 
