HERBERT R. O'CONOR, GOVERNOR. 1547

shall, nevertheless, have the right to enter and inspect all
mines where from two to five persons are employed or engaged
in work for the purpose of determining the conditions of safety
in any such mine. In case a mine inspector shall find any such
mine to be unsafe, or to be operated in any unsafe manner, he
shall order such unsafe conditions to be forthwith corrected,
and in default of the owner or operator doing so, shall order
such mine closed until the unsafe conditions are corrected.

"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 repre-
sentative 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 approxi-
mately vertical, extending downwards from the surface; and
shall include an underground shaft driven between two levels.

"Slope" includes an inclined opening in a dipping coal
and/or fire clay bed and an inclined tunnel to a coal and/or
fire clay bed.

"Superintendent" means the person who shall, on behalf of
the operator, have immediate supervision of one or more
mines.

"Tunnel" means a level or inclined passageway driven
mainly through barren strata. It may or may not come to
the surface.

"Ventilating Current" means a current of air circulating
throughout the mine excavations, of such purity that it shall
contain not less than 19 per cent, of oxygen nor more than
(l¼) one and one-fourth per cent, carbon dioxide. The dis-
trict mine inspector shall, whenever he has reason to suspect
an excessive proportion of carbon dioxide, or insufficient
oxygen in the atmosphere of any mine, take such tests as the
Bureau may prescribe, and upon disclosure of a ventilating