Royal Society of Edinburgh. 153 
tion on the days following the 4th of February, when engaged in re- 
pairing some damage which had then occurred to the electric wires 
connecting the Nelson Monument and the Observatory; and finding 
that plumbers (employed by the Town-Council) were removing the 
old lead and substituting new in its place, and being also encouraged 
by Professor P. G. Tait, who with me visited the spot, to believe 
that the markings which had been discovered were electrically of 
unusual interest, I lost no time in applying to Mr J. D. Marwick, 
town-clerk, for those portions of the leaden covering which con- 
tained the marks in question, with the view of presenting them to 
the Royal Society. 
Mr Marwick was as obliging as prompt in responding to such a 
request, and sent me the required specimens next day, accompanied 
by the enclosed memorandum written by Mr H., assistant to 
Mr Cousin, city-architect. 
10th February 1863. 
“The accompanying pieces of lead were taken from the north- 
west side of the lead platform on the roof of the lower part of 
Nelson’s Monument. 
“The distance between the holes was about nine feet six inches. 
“ Both holes were immediately over a block-tin gas-pipe, which 
is here carried under the lead and boarding of the platform, and 
which was found melted the whole length between the two holes, 
and a foot beyond the north-east hole. 
“These holes in the lead were evidently directly caused by the 
porning: gas from the pipes underneath. 
Fig. 1. 
Sl = es aes POLE’ 
LLL, BOAR DING 
ot 
Jyld FHL 
40 
Y WY oe. 
“The sketch shows section through the platform between the 
two holes A and B. CD shows the gas-pipe under and between 
them. 
“ From this sketch we might naturally expect a hole melted in 
the lead at A, the pipe being here at its highest level immediately 
under the boarding, only one inch from the. lead. 
“The pipe between C and D would very quickly be melted by 
the burning gas, as it lies horizontally and can be more easily acted 
on by a flame issuing from it. 
“ At D the pipe dips vertically about eighteen inches. 
“Tt is evident that the vertical length of pipe DE would not 
be readily melted by the strong flame burning at D. 
“The boarding and lead at B, immediately over D, would there- 
NEW SERIES.— VOL. XVIII. NO. I.— JULY 1863, U 
