Page:Dictionary of aviation.djvu/229

 DICTIONARY OF AVIATION 305

or atmosfere, as a small secondary balloon used by aero- nauts for detecting air^currents at some distance from the main balloon.

2. a small unmand hydrogen^fild balloon, now usually made of thin rubber, carrying meteorological instruments and dispatcht to great altitudes where the gasbag usually explodes allowing the instruments to descend slowly by the aid of a parachute; a ballon sende.

source soics n. a hypothetic point or system of peints at which fluid is being continually generated or produced : the epposit of sink.

line source, a source in the form of a line; a linear source.

point source, a source consisting of a single point. sour cetand* sink system, a hypothetic system in which fluid is being produced (at a source) and made to dis- appear (at a sink).

span spaen n. the transverse dimension of an aeroplane or other aerofoil; tip?to^tip mesurement; extent of stretch; expanse; spred (sense j).

spar spa:z n. a stick or piece of wood of considerable length as compared with its thickness, forming some part of an airship, as a strut, mast, or brace; a round stick of timber; a pole.

spark-break 'spaiok^zeek n. the break or breaking of the electric circuit at the spark-gap of an internakcombustion engin, in the make^and^break system of ignition.

spark-gap 'spa:zk,gaep n. the gap or open space between the electric terminals where the sparks are formd which are used in the make?and?break system of ignition.

speaking-trumpet 'spii-kirj,trAmpit n. a trumpetelike in- strument used for speaking at a distance; a megafone.

spear-kite 'spi:z,kait n. a kite whose frame consists of two sticks of unequal length crest at right angles, and which therefore resembles in shape the hed of a spear.

specter 'spektaz n. [also spelt spectre! a startling cloud* effect in which the observer sees his own shadow cast upon the clouds or en thin feg (with a circle of glory around the hed).

speculum 'spekc.u-tem n. [plural specula, speculums] an ocel- lus or eye^spet, as of a peacock's tail; also, the mirror of a wing, a specially colord, often iridescent area en some of the flightff ethers ; the mirror.

speed spiid n. rapidity of movement; swiftness; velocity.

air speed, the speed of a flying^machine relativ to the air thru which it is passing : distinguish! from land speed.

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