438 
The foregoing results agree in their main features with 
those obtained by Professor Kreil* and Mr. Broun, from the 
discussion of the Prague and Makerstoun observations. The 
chief difference is in the winter lunations. In the Prague ob- 
servations the lunar variation is extremely small in winter, and 
its law is apparently masked by irregular changes; while at 
Makerstoun there is but one maximum and one minimum in the 
winter months, and the magnet deviates but once to the east 
and once to the west in the course of the day. It seems difficult 
to reconcile such influences of season with any physical cause. 
It now remains to examine the consistency of the fore- 
going results with those already obtained, on the dependence 
of the diurnal range of the declination upon the moon’s age. 
It is obvious that as the periods of the oscillations caused 
by the sun and moon respectively, in the position of the freely 
suspended magnet, are different, they will combine in every 
variety of phase; so that the resultant oscillation will vary with 
the moon’s age in the course of the month. Let the variation 
of the declination at any hour, caused by the sun and moon 
respectively, be denoted by Aw and du; then m and n being 
the solar hours of greatest and least declination, and p the in- 
terval (in hours) between the sun and moon’s meridian pas- 
sage, m—p and x—p will be the corresponding lunar hours, 
and the resultant range will be 
Anu- Anut On p uU— a U. 
The values of this quantity are given in the following Table, 
—in the first column of which are the days of the moon’s age ; 
in the second the corresponding hours ( p) of the moon’s re- 
tardation ; in the third and fifth the calculated values of 
* The author takes this opportunity of stating that, in referring to Pro- 
fessor Kreil’s labours on this question in his former communication, he omit- 
ted to notice the elaborate memoir, “ On the Influence of the Moon on the 
Magnetic Declination,” read to the Imperial Academy of Sciences in Vienna, 
in 1850, and published within the last year. Had he read that paper before 
he had written his own, he could not have questioned the sufficiency of the 
evidence for the lunar action which it contains. 
