302 
MR, airy’s account OF THE HARTON EXPERIMENT 
required for fixing these wires and for other adjustments of the galvanic apparatus, 
was contributed gratuitously by the Electric Telegraph Company; the work being 
done under the direction of their resident agent at Newcastle, Mr. Mathews. 
14. The local arrangements being thus brought to a very satisfactory state, I had 
next to provide the proper apparatus. On my request, through Colonel Sabine, 
Treasurer of the Royal Society, the Council of the Society immediately placed at my 
disposal the instruments which they possessed and which applied to ray wants. These 
were two invariable pendulums, both by Thomas Jones (distinguished by the marks 
“ 1821 ” and “ No. 8” respectively), which were preserved in the Kew Observatory ; 
iron stands for the pendulums, accompanied by wooden stands for the comparison 
clocks, preserved in the Magnetic Office at Woolwich ; and a clock by Shelton 
(which I had formerly used in Cornwall, and which still bore my paper marks upon 
its pendulum). To these I added a clock by Earnshaw (from the east dome of the 
Royal Observatory) ; a journeyman-clock (from the Royal Observatory) to be used 
in signal-transmission; two galvanometers, similar to the ordinary speaking-needle 
of the galvanic telegraph ; galvanic batteries ; barometers, thermometers, &c. Every 
instrument was brought, for trial, to the Royal Observatory. 
15. Each iron stand consists of a horizontal triangle of iron bars for base; two 
inclined iron bars in a vertical plane for front, their tops being screwed to the sides 
of an iron box-frame which supports the agate-frame on which the knife-edge 
vibrates ; and one inclined bent iron bar behind, screwed to the back of the same 
box-frame. On erecting one of the iron stands at the Royal Observatory, it was 
found impossible to pass the upper brass block of the pendulums (to which the steel 
knife-edge is screwed) through the holes of the box-frame. It was necessary there- 
fore to enlai’ge the holes by filing ; and as this weakened the front of the box-frame, 
the following apparatus was introduced in order to strengthen it. A small hexagonal 
iron frame was prepared, consisting of a horizontal base nearly equal in length to the 
interior measure of the box-frame, two vertical sides nearly half the height of the box- 
frame, two inclined sides, and a horizontal top about one-third as long as the bottom. 
Screws were tapped through the horizontal base. This apparatus was placed in the 
front opening of the box-frame ; and, when the screws were driven, the short horizon- 
tal top was forced up to the upper bar of the box-frame so as to give it all desirable 
firmness. As the weakened stand, furnished with this apparatus, was evidently firmer 
than the other stand, a similar apparatus was provided for the other stand. 
16. The agate-planes, and the knife-edges (which were much injured by rust), were 
reground and polished by Mr. Simms with the utmost care ; the knife-edges being 
finished to an angle of about 120°. On mounting them at the Royal Observatory, it 
was found that they touched the agate-planes only in a few points ; and the singularity 
of the mode of contact reminded me so strongly of the contact in Cornwall in 1828, 
that I do not doubt that one pendulum was the same and affected by the same faults. 
A few interchanges, &c. of pendulums showed that the fault was not in the agate- 
