Abstract: A scale formation-inhibitory agent used in a welding treatment comprises a polymer selected from the group consisting of polymers having oxygen atoms in the main chain and polymers capable of being thermally depolymerized. The scale formation-inhibitory agent can inhibit the formation of scale on the surface of a metal part to be welded during a welding treatment.

Abstract: A projection type display apparatus comprising three projection units for projecting red, green and blue images, each having a constitution wherein a holding member for holding a CRT and a holding member for holding a projection lens are separately constituted and these holding members are connected liquid-tightly by means of a soft packing sheet, while a space surrounded by the holding members and the packing sheet is filled with a coolant liquid.

Abstract: Projecting-type display apparatus, wherein an image forming means frame is supported in such a manner as to be rotatable within a first plane perpendicular to an optical axis of a projection lens, and within a second plane including the optical axis and perpendicular to the first plane. A projecting-type display apparatus comprising means for changing the distance between an image forming means frame and a lens frame continuously or stepwise. A projecting-type display apparatus comprising means for changing the field angle of a projection unit having image forming means and projection lens with respect to a sreen cointinuously or stepwise.

Abstract: A magnetic recording/reproducing apparatus incorporating a clogging detector includes comparator for comparing with a predetermined value an absolute value of signals which are produced by reproducing recorded signals immediately after recording. Clogging signals may be supplied to cleaner for cleaning heads when the absolute value is less than the predetermined value.