MAGNETIC INCLINATION AT GOTTINGEN. 625 
quite agree; probably the result with the second needle has 
been made 30" too small by an error of the press. I do not 
know the particular locality of the observation of 1805; that of 
1826 was taken in the open field some hundred paces east of 
the Astronomical Observatory. 
Forbes’s observations are printed in th Transactions of the 
Royal Society of Edinburgh, vol. xv. part 1. pp. 31 and 32 ; they 
were made in the garden of the Astronomical Observatory with 
an instrument of Robinson’s of smaller dimensions than mine, 
having two needles six English inches in length: the observer 
himself regards the second needle as the best of the two. 
I have not included in this series the observations made by 
Mayer in March 1814, and recorded in the Commentationes re- 
cent. Soc. Gotting., vol. iii. pp. 36, 37, because they are unde- 
serving of confidence. The example which Mayer himself gives 
in p. 35 shows how very imperfect was the instrument used by 
him; its place being unchanged, it gave in ten partial results 
differences of more than a degree. Even the final results on two 
different days differ half a degree. 
My own observations of June 23, 1832, recorded in p. 44 of 
the Intens. vis Magnetice Terrestris, is equally undeserving of a 
place here, as well on account of the imperfection of the instru- 
ment, as on account of the place of observation which was in the 
Astronomical Observatory, where iron at no great distance 
materially affected the result and appears to have produced an 
increase of inclination. 
These inclinations admit of being brought into very good ac- 
cord by means of the assumption of an annual uniform decrease 
of 3 minutes (or more exactly of 3! 2!-3), if in Forbes’s obser- 
vations we keep to the result with the second needle; and there 
then remains only such differences as we may well ascribe to the 
combined influence of errors of observation and of fluctuations 
of the inclination. As however it appears from Hansteen’s in- 
vestigations on observations at other European stations, that the 
yearly decrease has gradually become less, we should regard the 
number above given rather in the light of a mean value corre- 
sponding to about the epoch of 1829, awaiting from future ob- 
servations the confirmation and more exact determination of its 
non-uniformity, 
