Lovering and Bond on Magnetic Observations at Cambridge. 23 
has just passed over in seven hours. Again, the arc traversed by 
the bar in its daily excursions varies perceptibly from one day to 
another; but the approximate law is, that in the six months from 
the vernal to the autumnal equinox, its value is between 13/ and 
15’; and in the remaining six months the mean of the daily arc is 
between 8’ and 10’. But there may be single days when it 
amounts to 25’ and others when it is as small as 6’. 
Gauss thinks that eight A. M. and one P. M. of mean solar time 
are never far from the periods of daily minimum and maximum dec- 
lination in Gottingen and that part of the globe. It appears from 
a Report in regard to the magnetic state of the Russian empire 
for 1837 * that, at St. Petersburg, the greatest westerly position of 
the north end of the magnetic meridian is near two o’clock, P. M. 
and the opposite position is at eight in the morning with the excep- 
tion of November, December, and January, when it occurs later. 
This is easily explained by the high latitude of the place when we 
come to consider the dependence of this daily motion on the sun. 
Since the declination is easterly in some parts of Russia, it follows that 
the maximum declination there is in the morning and the minimum 
in the afternoon. As the Report in question has been published 
with great care we extract a Table of the Monthly Means of the 
are of daily excursion to show how near they correspond to the 
more extended means which we have mentioned above. 
* Annuaire Magnetique et Météorologique du Corps des Ingénieurs des 
Mines de Russie. Année 1837. St, Petersburg. 1839. 
