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law of disturbance being superposed on the general law of mean 
daily variation. 
13 th, It follows from these results, that the daily mean absolute 
intensity of the whole earth is not a constant quantity, but that it 
increases as a whole, and diminishes as a whole, from day to day. 
14^, In the examination of the usual daily means for the years 
1842—48 (though the years 1844—45 only are considered in this 
paper), it appears that there is a period of about 26’2 days on the 
average, which is felt equally (within the limits of errors of co- 
efficients) and simultaneously at all the stations. This period was 
remarked by the author in his discussion of the Makerstoun Obser- 
vations for 1844-45 ; it was attributed at that time to the action of 
the moon, and the law obtained connected with its synodical revolu- 
tion. The author gives grounds to show that it is probably due to 
the sun. The identity of the movement at all stations at the same time, 
whatever may be the position of the moon, would of itself disprove 
the connection of our satellite as the cause of this period. An ex- 
amination of a larger series of observations than that considered in 
this paper will show that the minimum frequently takes place at 
full moon, as well as at new moon. 
15 th 7 The author has avoided theoretical speculations in his paper, 
but he believes that the moon acts as a secondary cause, the large 
disturbances occurring most frequently near full moon. This fact, 
he thinks, hypothetically, may be connected with an electric fluid 
emanating from the sun, acted on by the planets, and drawn towards 
the earth most powerfully when the moon is in opposition. This 
action does not prevent, though it occasionally masks, the period due 
to the rotation of the sun itself, and the unequal electrical tension 
of its different sides — this difference being also probably connected 
with the solar spots. It is obvious that should the moon and planets 
act in the way supposed, the period due to the sun’s rotation will 
appear to vary within certain limits, independently of the sup- 
position that the suiTs side of greatest tension is variable. Such an 
hypothesis would connect the secular variations with the electrical 
tension of the sun, and the periods of the planets. The author pro- 
poses to consider this question more at large hereafter, in a discussion 
of all the observations from 1840 up to the present time. He con- 
cludes by noticing the appearance of a period of about sixty to seventy 
hours in the daily mean variation. 
