446 0. N. Rood—Application of the Horizontal Pendulum to the 
the pendulum, after a had once come to rest, to obey impulses 
from without more tardily than was quite right. To obviate 
this possible difficulty I afterward provided the pendulum with 
a paddle instead of a wire, and caused the former to move 
loosely like a piston in the interior of a suitable box, which 
was entirely submerged in kerosene oil; the results were very 
promising, but I have not had time to use this method in an 
extended set of experiments. 
At SS, figs. 8 and 4, are stops which confine the motion of 
the pendulum within narrow limits; 
K they consist of spiral springs, which 
= are fastened in the prolongation of 
Seana adjusting screws. Thesprings form 
an essential part of this indispensa- 
ble arrangement, and without their 
aid it was often found impossible to 
complete the leveling, so as to give 
the instrument even a moderate de- 
gree of sensitiveness. 
At I, figs. 3 and 4, is shown an 
index or pointer, intended to facili- 
tate the adjustment of the pendu- 
lum with regard to the scale, and 
readily bring it into the zero of po- 
sition. It makes a very convenient addition, and is observed 
by a lens placed outside of the glass case enclosing the whole 
apparatus. 
may here remark, that the above-mentioned additions 
ought hereafter to be made to the horizontal pendulum, even 
when constructed solely for astronomical purposes, the oil-box 
being replaced by an air-box, contrived so as to reduce the 
tendency to oscillate. mpare Tépler, “Ueber einige An- 
wendungen der Luftreibung bei Messinstrumenten,” Pogg. 
Ann., 1878, xlix, 416. 
l of suspension.—In the first experiments fine iron wire 
was employed, but it was soon found that its presence rendered 
accurate magnetic observations impossible; and besides, al- 
though it was as fine as was consistent with safety, its torsion 
was noticeable. I afterward replaced it with narrow strips of 
elastic copper-foil, such as is used by jewelers, the ends being 
soldered to small thin plates of brass to prevent tearing, and 
these again connected with fine, hard-drawn brass wire. The 
copper-foil was adopted merely as a temporary expedient, but 
as it was found to answer well, and to be free from sensible 
torsion, it was retained. Experiments were made beforehand 
on its strength, and it was loaded up to within about two-thirds 
of its breaking strain. 
