MAGNETIC INCLINATION AT GOTTINGEN. 627 
The task is greatly facilitated by an apparatus which I did not 
have made until afterwards, and which serves to bring the sur- 
faces of the agates into one plane, and to make this plane hori- 
zontal: I will not however stop to describe it in this place, as 
it could not be employed for the present observations, with the 
exception of those of the 23rd of September. A second contri- 
vance, which also was not completed until after the conclusion 
of the observations, serves for the accurate determination of the 
deviation of the principal circle from the vertical position. A 
deviation of ten minutes has thus been found: this could not be 
removed without altering the putting together of the instrument : 
its influence on the inclination however cannot amount even to - 
a second. 
Further, I must not omit to notice, that small errors in the 
different adjustments can only produce a nearly imperceptible 
effect on the determinations of inclination. The influence which 
some of the errors have on the position of the needle, is, in re- 
spect to that position, only a magnitude of the second order ; 
and the effects of the others, 7. e. of an excentricity, and of an 
inclination of the tangential plane to the agates in the sense 
parallel with the plane of the circle (faults against conditions 3, 
6 and 4), are perfectly eliminated by the combination of the 
partial observations. I cannot therefore agree in the opinion 
expressed by Horner (Physik. Worterb. 5 Band. 8. 759), that 
the removal of this latter error ought to be looked to before all; 
on the contrary, I regard its perfect removal as that which is of 
_ the least importance. . 
6. 
The observations of inclination here given were all made on 
the spot described in vol. v. of the Resultate, protected by a shed 
from the rays of the sun. The instrument was placed on the 
stone in such manner that the line joining two of the feet should 
be nearly perpendicular to the magnetic meridian ; and for this 
position the places of the three feet were marked. The exact 
magnetic orientation of the instrument was obtained by means 
of an auxiliary needle supplied with it, suspended by a small 
inverted agate cup which rested on a point; the frame-work 
carrying the point has two short cylindrical side arms which 
are laid in the two Y’s, so that the point takes of itself a ver- 
tical position. I have several times combined with this method 
the other usual one, of corresponding inclinations in two posi- 
