34 Lovering and Bond on Magnetic Observations at Cambridge. 
the same time on the several days and dividing by 5. The result 
is the mean temperature for that period of the day. Then the 
times of maximum and minimum of the mean curve are found from 
the greatest and least values of these mean results. The absolute 
variations of temperature from one day to another vitiate to a cer- 
tain extent this process. The same method is pursued for laying 
down the mean diurnal magnetic curves; the absolute changes 
of magnetic declination from one day to another are too inconsid- 
erable to produce any great error in the result. But the mean of 
the daily magnetic curves is materially injured by the irregular 
perturbations of the magnetic meridian. Hence it is supposed that 
the mean thermometric curves have a fair comparison with the mean 
magnetic curves. For the sake of facilitating this comparison, the 
following abstract is given of the single and mean diurnal magnetic 
curves which are drawn at length on Plate IV. 
Date. Time of Mini. | Renita of tho | Time of Maxi- | featines of the (Besbents 
mum Declination. mum Declination. Daily Range. 
Civil Time. |Cambridge M. ‘I’. Scale. |Cambridge M. T. Scale. 
October 21) 8" 6’A.M.} 102.562 | 0°28'P.M.) 92.354 10.208 
Sis OF 836 © 104.333 11 46A.M.| 93.364 10.969 
< 23), 9ial tae 103.375 | 2 51P.M.| 96.031 7.344 
uy 243 16" ss TOS208™ | 273i 5 6 95.396 7.812 
ce Qoioal ieee 101-7405) 141 92.302 9.438 
Means |752 “ | 103,044 |127 “ | 93.889 | 9.154 
Meancurvel8 36 “ | 102.250 1a 1 “ | 94.368 | 7.882 
We have now the following results of comparison : 
Times of maximum temperature range from 11" —A. M. to 2 40’ P. M. = 3" 40/. 
fe « declination “ Se AGI to) 2 aac. 
‘ of minimum temperature “ ceo “« to6 50 A.M.=5 50. 
cs a declination “ a too u lees st hours. 
It appears, then, that the times of maximum and minimum magnetic 
declination are comprised within narrower limits than those of the 
