P. E. Chase on Meteorological Comparison. 159 
ave 2 limited local origin, and less affected by sudden violent 
disturbances, It seems reasonable, therefore, to suppose that 
the oscillations about the mean magnetic values should differ, in 
duration and in other respects, from those about the thermal and 
barometric means. If their mutual relations are much obscure 
IM consequence of this difference, any lingering evidences of 
7 aan that we may find may be entitled to great 
weight. 
at Toronto ; 1843, 45, ’46 at St. ; the observations of 
ing comparatively incomplete), the average duration of 
the fluctuations of each ele I found the following mean 
a | Bee Se ee OS ee aa ee 
Toronto, . 3°98 days. | 3-93 days. | 4°54 days. |. 4°31 days. | 3°10 days, 
St. Helena, | 4:38: < | se7 * | 392 “ | 446 * | 335 * 
_ The mean wave-periods, taking the duration of the alternate 
Variations above and below the monthly means, were as follows: 
a B. peor H. | Vv. | ee 
Toronto, .. | 2-91 days. | 3°70 days. | 4°65 days. | 4°78 days. | 2°32 days. 
St. Helena, 3-76 ee 8:86 “ 4°34 “ 551 7 3°27 “ 
By marking with the signs + and — the excess or deficiency 
of each daily mean, the monthly mean being assumed as the 
Standard of comparison, I obtained the data for Tables I and IT. 
The columns headed C contain the me of observations that 
‘sent a correspondence (excess in one element accompanying 
__-©Xcess in the shoe and ft versa), and those headed O give the 
_ Bumber of instances in which there was an opposition of a ke 
between the daily means indicated by the heading of each dou le 
