A double-headed piston type compressor connected with an external device is provided. An image of the beam is projected onto an array of charge-coupled devices parallel to the line for detecting anomalies andor features of the surface, where the array is outside the plane of incidence of the focused beam. for absorbing the one or more sulfur compounds. The gauge section 24 preferably has an axial length at least 75% of the bit diameter. The fixed hinge connects the second sections so that they are rotatable with respect to each other.