204 A. D. Bache on Declinometer Observations. 
stations chiefly determine the double crested character of the 
curves of di - 
ag 
O 
russels, Greenwich, Dublin, etc., for instance, exhibit two 
ne alte 
<ima, 
mallér, about the summer solstice. The system to which 
of the secular change, and it was then shown that the Philadel- 
hia observations share in this respect a similar difficulty with 
other stations in consequence of which the results must be Te 
ceived with caution.* 
_ In the mean monthly values of the declinometer readings and 
in their differences, when compared month for month, are com- 
bined the joint effect of the secular change, and of the annual 
inequality. To eliminate the effect of the secular change, condi- 
tional equations were formed, which give a value deduced by the 
eats of the method of least squares, of 1-227 divisions, 28 
he monthly effect of the secular change.t The effect 0 the 
secular change was deduced from the mean monthly values, and 
* Dr. Lloyd's instruetive note on this subject in his discussion of the Dublin ob- 
pare is as follows: “ The siiciebatign of the annual variation is much more 
ifficult than that of the diurnal, both on account of the much smaller 
of the period and the difficulty of preserving the instrument in the same un 
condition during the much Ionger time, or of determining and allowing for its 
changes when they do occur; ingly, although the annual period may traced 
in the observations of Gilpin and is Seared in those of Bowditch, it 
rese f recent Th indi of its 
existence in the Gottingen observations, which w A. 
1 p.m., and Prof, Gauss and Dr, Goldsmith, find in the analysis of these observations 
no important fluctuations iy ag upon season. A lar negative result is de- 
duced by Dr. Lamont from Munich observations which were made twelve times 
a day. 
+ This value '6’7 of annual change, tho not preferable to alue (4/5) de- 
—* Pegs method in n lof this pe ae a Pala Mera far 
loyed in the present investigation. The most reliable value 5”-0 was deduced 
re independent observatious, as already announced. — 
. 
