Lighining Conductors in Ships. 347 
_ The national road crosses the Monongahela at Brownsville, sixty 
miles (following the stream) above Pittsburgh. This village is found- 
ed on a bed of coal, of a quality superior to that of Pittsburgh; the 
precipitous banks directly opposite, present the first limestone in strata 
which I met with, but no coal is near, nor is any limestone found on 
the Brownsville side, unless in thin layers high above the coal. 
From this to Washington, Penn., the country becomes more level, 
and the coal banks are less frequent. There we turned off the na- 
tional road to Pittsburgh, distant twenty six miles. The banks of 
Chartier’s creek, which we crossed three or four times, are full of 
fine coal, which is hauled six miles to supply the borough of Wash- 
ington and its neighborhood. I have memoranda that may enable 
me at a future time, to give you further particulars relative to this 
immense coal formation and its attendant strata, but you must be at 
present satisfied with this crude and hasty sketch, and a parady of 
your remark, published in the XIX Vol. of the Journal of Science, 
relative to the anthracite in the eastern section, * that the sun and the 
bituminous coal of Western Pennsylvania will burn out together.” 
Arr. XVI.—On the Utility of fixing Lightning Conductors in Ships ; 
by W. S. Harris, Esq. Member of the Plymouth Institution. 
[From the Edinburgh New Philosophical Journal.] 
1. A rHunpeER-sTorm is the result of a great natural action sub- 
Sisting between an extensive stratum of cloud, and a corresponding 
portion of the earth’s surface, together with the intervening atmos- 
phere; and is the result of some powerful agency, the nature of 
Which is as yet undiscovered. 
2. The active principle of a thunder-storm, however, may be con- 
sidered as an extremely subtle species of matter universally pervading 
nature, and distributed in bodies, in quantities proportionate to their 
Capacities for it, so that when accumulated in and about certain bod- 
ies, and abstracted at the same time from other bodies, a tendency 
fo regain the previous state of proportionate distribution is marked 
Y @ certain train of phenomena ; thus, a concentrated action is fre- 
quently set up between the overcharged and undercharged bodies, 
Which produces all the effects of a violent and terrific expansive 
force, for the original state of proportionate distribution is often re- 
Stored by a rapid explosion, at which instant the most compact bod- 
