Part 193

Pho`to-etch"ing, n. A photo- engraving produced by any process involving the etching of the plate.

Pho`to*gram"me*ter (?), n. [See Photogram; -meter.] A phototheodolite, or a camera designed for use in photogrammetry. -- Pho`to*gram*met"ric (#), Pho`to*gram*met"ric*al (#), a.

Pho`to*gram"me*try (?), n. [Photogram + metry.] A method of surveying or map making by photography, used also in determining the height and motions of clouds, sea waves, and the like.

Pho*tog"ra*phone (?), n. [See Photograph; -phone.] A device, consisting essentially of an electric arc and a camera, by which a series of photographs of the variations of the arc due to sound waves are obtained for reproduction by means of a selenium cell and a telephone.

Pho`to*he`li*om"e*ter (?), n. [Photo- + heliometer.] (Astron.) A double- lens instrument for measuring slight variations of the sun's diameter by photography, utilizing the common chord of two overlapping images.

Pho`to*lu`mi*nes"cent (?), a. [Photo- + luminescent.] (Physics) Luminescent by exposure to light waves. -- Pho`to*lu`mi*nes"cence (#), n.

{ Pho*tom`e*tri"cian (?), Pho*tom"e*trist (?) }, n. A specialist in photometry.

Pho`to*mez"zo*type (?), n. [Photo- + It. mezzo middle, half + -type.] A photomechanical process similar to collotype.

Pho`to*neph"o*graph (-nf"*grf), n. [Photo- + Gr. ne`fos a cloud + -graph.] (Meteor.) A nephoscope registering by photography, commonly consisting of a pair of cameras used simultaneously.

Pho*toph"i*lous (?), n. [Photo- + Gr. &?; loving.] (Phytogeog.) Light-loving; growing in strong light, as many plants.

Pho"to*phore (?), n. [Photo- + Gr. &?; to bear.] 1. (Med.) A form of endoscope using an electric light.

2. (Zoöl.) A light-emitting organ; specif., one of the luminous spots on certain marine (mostly deep-sea) fishes.

Pho"to*play` (?), n. A play for representation or exhibition by moving pictures; also, the moving- picture representation of a play.

Pho"to*print` (?), n. Any print made by a photomechanical process.

Pho`to*syn"the*sis (?), n. (Plant Physiol.) The process of constructive metabolism by which carbohydrates are formed from water vapor and the carbon dioxide of the air in the chlorophyll-containing tissues of plants exposed to the action of light. It was formerly called assimilation, but this is now commonly used as in animal physiology. The details of the process are not yet clearly known. Baeyer's theory is that the carbon dioxide is reduced to carbon monoxide, which, uniting with the hydrogen of the water in the cell, produces formaldehyde, the latter forming various sugars through polymerization. Vines suggests that the carbohydrates are secretion products of the chloroplasts, derived from decomposition of previously formed proteids. The food substances are usually quickly translocated, those that accumulate being changed to starch, which appears in the cells almost simultaneously with the sugars. The chloroplasts perform photosynthesis only in light and within a certain range of temperature, varying according to climate. This is the only way in which a plant is able to organize carbohydrates. All plants without a chlorophyll apparatus, as the fungi, must be parasitic or saprophytic. -- Pho`to*syn*thet"ic (#), a. -- Pho`to*syn*thet"ic*al*ly (#), adv.

{ ||Pho`to*tax"is (?), Pho"to*tax`y (?) }, n. [NL. phototaxis; photo- + Gr. &?; an arranging.] (Biol.) The influence of light on the movements of low organisms, as various infusorians, the zoöspores of certain algæ, etc.; also, the tendency to follow definite directions of motion or assume definite positions under such influence. If the migration is toward the source of light, it is termed positive phototaxis; if away from the light, negative phototaxis. -- Pho`to*tac"tic (#), a. -- Pho`to*tac"tic*al*ly, adv.

Pho`to*te*leg"ra*phy (?), n. Telegraphy by means of light, as by the heliograph or the photophone. Also, less properly, telephotography. -- Pho`to*tel"e*graph (#), n. -- Pho`to*tel`e*graph"ic (#), a.

Pho`to*tel"e*scope (?), n. (Astron.) A telescope adapted for taking photographs of the heavenly bodies.

Pho`to*the*od"o*lite (?), n. An arrangement of two photographic cameras, the plates of which may be brought into exactly the same plane, used in surveying and map making. From the differences between two pictures taken at the same moment, measurements in all dimensions of the region may be obtained.

Pho`to*ther"a*py (?), n. (Med.) The application of light for therapeutic purposes, esp. for treating diseases of the skin. -- Pho`to*the*rap"ic (#), Pho`to*ther`a*peu"tic (#), a.

Pho`to*ther"mic (?), a. Of or pertaining to both light and heat.

Pho*tot"o*nus (?), n. (Physiol.) An irritable condition of protoplasm, resulting in movement, due to a certain intensity of light. -- Pho`to*ton"ic (#), a.

Pho`to*to*pog"ra*phy (?), n. Photogrammetry. -- Pho`to*top`o*graph"ic (#), Pho`to*top`o*graph"ic*al (#), a.

Pho`to*tri`chro*mat"ic (?), a. [Photo- + tri- + chromatic.] Designating a photomechanical process for making reproductions in natural colors by three printings.

Pho*tot"ro*pism (?), n. [Photo- + Gr. &?; to turn.] (Plant Physiol.) The tendency of growing plant organs to move or curve under the influence of light. In ordinary use the term is practically synonymous with heliotropism.

Pho`to*vis"u*al (?), a. (Optics) Of certain achromatic lenses, having the same focus for the actinic and for the brightest of the visual rays.

Phryg"i*an cap` (?). A close-fitting cap represented in Greek art as worn by Orientals, assumed to have been conical in shape. It has been adopted in modern art as the so-called liberty cap, or cap of liberty.

||Phy`co*my*ce"tes (?), n. pl. [NL.; Gr. &?; seaweed + mycetes.] (Bot.) A large, important class of parasitic or saprophytic fungi, the algal or algalike fungi. The plant body ranges from an undifferentiated mass of protoplasm to a well-developed and much-branched mycelium. Reproduction is mainly sexual, by the formation of conidia or sporangia; but the group shows every form of transition from this method through simple conjugation to perfect sexual reproduction by egg and sperm in the higher forms. -- Phy`co*my*ce"tous (#), a.