MAGNETIC INCLINATION AT GOTTINGEN. 629 
fourth part of its amount was, with only slight variations—four- 
teen minutes. The observations of vibration were always taken 
in the astronomical observatory upon a stone pedestal, the object 
being not so much the determination of the absol ite time of 
vibration as of its relative amount, which cannot be sensibly 
affected by the slight local influences which may possibly exist 
there. 
ro 
In the observations of inclination in the summer of 1842, L 
had in view, besides the establishment of the magnetic incl'- 
nation corresponding to that epoch, the determination of the 
degree of precision attainable with the instrument employed. 
It did not appear to me that the trustworthiness of a final 
result, which is influenced by so many circumstances, could be 
sufficiently estimated from the differences in the position of the 
needle in repeated raisings of the Y’s. The mere comparison of 
results, obtained on different days, is equally unsuitable for this 
object, as accidental errors are mingled with the actual fluctua- 
tions of the magnetic inclination itself. I was further desirous of 
learning whether my four needles were accordant, or wether, 
as has happened to some observers, they would give results 
having decided and important differences*. 
These considerations induced me to deviate from the arrange- 
ment usually followed, and to adopt another differing from it 
principally in the following particulars. 
It is usual to observe the position of the needle, i.e. the 
readings of the circle opposite the two extremities of the needle 
in four different combinations of the position of the circle, and 
of the mode of putting in the needle; the graduated face of the 
circle and the marked face of the needle being turned either 
towards the east or towards the west, and either to the same or 
to opposite quarters. These combinations are repeated after 
reversing the poles, producing in all sixteen numbers, of which 
the arithmetical mean is taken as the inclination, unless they 
show great differences arising from the centre of gravity of the 
* The most striking instance of this kind occurs in the Fifth Report of the 
British Association for the Advancement of Science, p. 142. Eight needles, em- 
ployed by Captain Ross, in determining the inclination in London, gave differ- 
encesof forty-one minutes, although the observations with each needle separately 
were numerous, and agreed well together. The reason of this remarkable fact, 
fuller details of which are not given, was supposed in England to have been 
the want of a perfectly cylindrical form in the axles, and moveable or revolving 
axles were tried on this account. 
