HARRY W. NICE, GOVERNOR. 335

voltmeter; or in case of a static charge, by an electrostatic
voltmeter.

Methane is a hydrocarbon gas (CH4) frequently encountered
in coal mines; when it is diffused through air in certain pro-
portions of the mixture, 5i/2 to 14i/2 per cent., the mixture will
explode in the presence of a flame or hot spark.

Mine includes the shafts, slopes, drifts or inclined planes
connected with the excavations penetrating coal and/or fire clay
stratum or strata, which excavations are ventilated by one gen-
eral air current, and all appliances and equipment for hoisting
and extracting coal and/or fire clay; and shall embrace any
and all parts of the mining property and plant on the surface
or underground, which contributes directly or indirectly to the
mining or handling of coal and/or fire clay; and which is con-
nected by one general system of mine railroads, over which
coal and/or fire clay may be delivered to one or more points
outside such mine. The word also includes a portion of a
mine when the sense so requires. The provisions of this sub-
title shall not apply to any mine employing less than five
persons excepting that the provisions of Section 54, Chapter 7,
Title V, Mine Management and Operations, requiring an
annual report in such form as the Bureau may prescribe, shall
apply to all mines without regard to the number of their em-
ployees.

Non-Gaseous Mine is a mine which has not been rated as
gaseous; or a mine which, having been rated as gaseous, has
been re-rated as non-gaseous as prescribed in the definition of
a gaseous mine, elsewhere in this section.

Operator means any firm, corporation, association or in-
dividual operating any coal mine or part thereof, whether as.
an owner, lessee or otherwise, and also includes the representa-
tive of such operator.

Panel means a unit area in a system of mining by which the
mine is divided into large rectangles or panels isolated or
surrounded by solid pillars of coal into which pairs of entries;
are driven for the development of rooms and the extraction of
pillars.

Permissible. Unless the context requires a different sense,
"permissible" means the admission of a device, plan, formula,
method, machine or course of action by the United States
Bureau of Mines to a list, after actual test thereof.

Potential and Voltage. These words shall be taken as
synonymous, to mean electric pressure as determined by the
voltmeter.

Shaft means an opening, the axis of which is approximately
vertical, extending downwards from the surface; and shall in-
clude an underground shaft driven between two levels.