MAGNETIC INCLINATION AT GOTTINGEN. 633 
the mean error of the difference between two means from five 
readings may be assumed 
i ee 
=/ laa 2 
and the mean error of a simple reading of one end of the needle 
_ f5 7994 
25-13 
This is certainly a very satisfactory degree of precision, and is 
not only confirmed, but sometimes even surpassed by a similar 
discussion of the observations on other days. It may be noticed, 
however, that the attainment of such an accord depends mate- 
rially on the circumstance of the needle never being raised until 
it is in repose, or very nearly in its position of rest. Without 
this precaution the needle, the vibration of which consists in a 
rolling of the axles upon the supporting planes, would come to 
rest on a different part of the plane from that on which it was 
let down, and thus the element of excentricity x would be a vari- 
able one. In the manner here given, the values of the elements 
of excentricity v and y are obtained, it is true, with much pre- 
cision; but these values cannot serve alone to instruct us 
whether and how much the supports and the Y’s must be 
moved, in order to satisfy conditions 3 and 6 in Art. 3, inasmuch 
as the latter refer to the centre of the inner circle, and the former 
to the centre of the graduation, which may not be, and in fact 
are not, the same in the instrument under consideration. The 
proper corrections of the adjustment were made with all possi- 
ble care previous to the observations here given. 
The value of z is evidently constant for each needle, and ac- 
cordingly a similar treatment of the observations on other days 
has given nearly the same value. For the three other needles 
TI found— 
= 39!-C. 
/ il 
for NEedIe Fi... 5.25 3 18 
Oat Eectaenc —1 4 
EM Dare is erat = Sa |e 
Although the knowledge of these values has no particular 
practical interest, yet their small amount is an honourable testi- 
mony to the care which the distinguished artist bestowed on the 
execution of the needles*. 
* [The dipping needles which have been made by Mr. Robinson's successor, 
Mr. Barrow, have proved in no respect inferior to those made by the excellent 
artist from whom M, Gauss’s instrument was procured.—L. S.] 
