Domed to Dovetaildado.

Domed. (PLast.) Showing a symmetri­cal distortion which makes a flat section of a plastic object appear convex, and a curved section more convex.
Dongola. (Leather.) Calfskin, goat­skin, or sheepskin tanned by the use of mineral and vegetable sub­stances, and finished to resemble French kid.
Door check. (Arch.) A device which insures the closing a door, the. movement of the door being re­tarded to guard against a too rapid closing.
Doorframe. (Arch.) The surrounding case in which a door opens and shuts.
Doorhead. (Arch.) The upper portion of a door frame.
Dope. (Aero.) Liquid material for ap­plication to the cloth surfaces of an airplane, to act as a filler, to in­crease strength, and to give tautness to the covering; resulting in an opaque finish.
Doppler effect. (Phys.) The apparent change in frequency of vibrations, as of sound, light, or radar, when the source or observer are in -mo­tion relative to each other. The fre­quency increases when the source is approaching the observer and diminished when it is receding. The principle is used In tracking and navigation systems.
Doping. Adding an impurity to a semiconductor to incre~se either the number of free electrons or of holes.
Dormer window. (Arch.) A small window projection from the slope of a roof.

Dormitory. (Arch.) A large sleeping room capable of accommodating many people. Also a separate build­ing used for sleeping.
Dosimeter. (Phys.) An instrument which determines the radiation dose a person has received.
Double-acting hinge. (Cabwk.. Carp., and Furn.) A hinge designed to pennit motion in either direc­tion as on folding draught screens, swinging doors, etc.
Double-action press. (Mach.) A press for handling two operations for each revolution of the press. It carries two rams, one inside the other, so actuated that one motion immediately follows the other.
Double belting. Belting formed of extra thick or double thickness of leather.
Double bond. (Chem.) Ethylene. ~C=CH2. In organic chemistry, a double linkage between two atoms of the Same element, one link fre­quently. stronger than the other.
1;)ouble-break switch. (ELec.) A switch which opens or closes the circuit in two wires at the same time.
Double-contact lamp. (Elec.) A lamp whose base has two bottom terminals which make contact when the lamp is inserted in the socket. .
Double-cut. (Shopwk.) Refers to double-cut file; i.e., one which has twe. rows of teeth crossing each other at an angle of 45 to 50 deg. The double-cut gives a broken tooth, the surface of the file hav­

Double demy. (Paper) Name given to drawing paper measuring 20 by 30 in.
Double-end bolt. (Mech.) A bolt hav­ing no solid head, being threaded at each end for the reception of nuts; often called a "stud" bolt.
Double-end trimmed. Lumber sawed square at both ends.
Double-rdament lamp. (Elec.) A lamp having two filaments, only one of which is lighted at a time. The fila­ments may be of the same or of different resistances, giving the same or different candle power.
Double-geared. (Mech.) A lathe or drill press equipped with an ordi­nary "back gear" is said to be dou­ble geared.
Double-hung window. (Arch.) A win­dow consisting of upper and lower sash, both carried by sash cord and weights.
Double ignition. (Auto.) See dual ig­nition.
Double-pitch skylight. A skylight sloping in two directions.
Double-point push button. (Elec.) A push button capable of controlIing two independent circuits at one operation, having one top and two bottom contacts.
Double roD. (Print.) When the ink rollers cover the form twice to each printing impression.
Double riveting. Two lines of riveting in a lap joint, or four in a butt
joint. (Ellgill.) A riveted joint made by two parallel rows
Double-row radial engine. (Aero.) An engine having two rows of cyl­inders arranged radially around a common crankshaft. The corres­ponding front and rear cylinders mayor may not be in line.
Double-seaming machine. (Sheet­Met. Wk.) A machine for turning up against the body of a vessel that flange which is left after the seam has been set.
Double-threaded screw. (Mech.) A
screw consisting of two distinct helices winding parallel with each other around the body; used to give an increase in the rate of travel;" seldom used in V or National threads.
Double-throw switch. (Elec.) A switch that can be thrown into two different positions, connecting one circuit to two different circuits but not at the same time.
Douse. To plunge into a liquid, as in quenching a piece of hot metal during a hardening process.
Douzieme. A unit of measure used by watchmakers. It equals .0074 inch.
Dovetail. (Woodwkg.) An interlock­ing joint. A tenon shaped like a dove's tail fits into a similarly shaped mortise. SEE PIN MEMBERS.
Dovetail cutter. (Shopwk.) Inner and outer dovetails are milled with this tool, and edges of work are con­veniently beveled.
Dovetaildado. (Woodwk.) A groove across a board cut so that the base is wider than the face of the

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