photochromy 
4454 
proximation is made to the natural appearance of the sub- 
ject. This process is peculiarly adapted to the reproduc- 
tion of such works of art as jewels, tapestries, potteries, 
and enamels. 
epiuastic movement or state of curvature ob- 
served in certain organs when exposed to in- 
tense light, due to a more active growth of the 
photochronograph (fo-to-kron'o-graf), . [< lorsal surface. Compare ; /,/ ( ,x^. 
P Gr. > ? * ), light, + E: cur,,,,.,',,, <<!,!,.] 1 . An photo-etching (to - to - ech mg) n. [< Gr. (toe 
- (0UT-), light, + E. etching.] Any process of 
photo-engraving or photogravure, or any plate 
or print produced by such a process, in which 
a subject in line is transferred by photography 
to a metal surface in such a manner that either 
the ground or the lines of the design will resist 
acid, with which the plate is then etched : most 
write.] "The'melhod, practice, etc.', oftaking commonly used for relief-plates on zinc,suchas 
instantaneous photographs at regular and gen- those of tue Glllet P rocess - See photo-enyrao- 
erally at short intervals of time, as of a bird, '-"'': 
horse, projectile, etc., in motion. 
photocrayon (f 6-to-kra'on), a. [< Gr. fyui; (<tor-), 
instrument for taking photochronographic pic- 
tures. See photochronography. 2. A picture 
taken by this method. 
photochronographic (fo-to-kron-o-graf'ik), a. 
Of or pertaining to photochronography. 
photochronography (fo'to-kro-nog'ra-fi), n. [< 
Gr. 0uf ((tor-), light, + xpuvoc;, time, + ypdtyeiv, 
or finished in crayons upon a photographic 
groundwork : said of a picture, 
photodermatic (f6"to-der-mat'ik), a. [< Gr. 
0<jf (<t>ur-), light, + tepfta, skin : see dermatic.] 
Having a luminous or phosphorescent skin ; 
phosphorescent, as the mantle of a mollusk. 
Nature, XL. 384. 
photodrome (fo'to-drom), n. [< Gr. (tof (<t>uT-), 
light, + dpo/iof, a running, < fpa^tlv, ran.] An 
instrument for producing optical effects by 
flashes of light thrown upon revolving disks on 
which are painted various figures or devices. 
photodynamic (fo"to-di-nam'ik), a. [< Gr. ^ 
((tor-), light, + diva/us, power: see dynamic.] 
Of or pertaining to the energy or effect of light. 
photodysphoria (f6"to-dis-f6'ri-a), n. [NL., 
< Gr. 0f (0uT-), light, + 6va<t>opta, pain hard to 
be borne: see dysphoria.] An intolerance of 
light; photophobia. 
photo-electric (f6"to-e-lek'trik), a. [< Gr. (jiuf 
(0<jr-), light, + E. electric.] Acting by the 
combined operation of light and electricity; 
producing light by means of electricity; also 
noting apparatus for taking photographs by 
electric light, or by a lamp whose illuminating 
power is derived from electricity. 
photo-electrical (fo'to-e-lek'tri-kal), a. [< Gr. 
<t>us ((k>r-),light, + E. electrical.] Same asphoto- 
electric. 
photo-electrotype (f6"to-e-lek'tro-tip), . [< 
Gr. ^wf (0ur-), light, + E. electrotype.] A pho- 
tographic picture produced in relief, such as to 
afford, by the ordinary processes of electrotypy, 
a matrix for a cast from which impressions in 
ink may be obtained. 
photo-engrave (fo"td-en-grav'), v. t. [< Gr. 
0uf (0ur-), light, + E. engrave.] To produce by 
or in photo-engraving. 
photo-engraving (f6"t6-en-gra'ving), n. [< Gr. 
0<yf (pur-), light, + E. engraving.] A common 
name for many processes by which a photo- 
graph may be made to afford a plate-matrix from 
which can be taken prints in ink corresponding 
to the original of the photographic image. These 
processes depend upon the property, possessed by potas- 
sium bichromate and analogous chemicals, of rendering in- 
soluble, under the action of light, gelatin or some similar 
body with which they are compounded. By applications of 
this property, varying according to the process, a picture or 
design can be produced on a metal surface, and the blank 
places etched out with acid ; or a matrix in relief can be 
formed, from which an electrotype plate can be made in or- 
dinary ways. In general, the term photo-engraving is lim- 
ited to a relief-block or -plate produced by photographic 
means for printing in an ordinary printing-press, to the art 
of making such blocks, and to prints from them ; while the 
term photogravure is commonly applied to a photographi- 
cally engraved plate in intaglio from which prints may be 
taken in a copperplate-press, to the art of making such an 
incised plate, and to a print from it. In the Gillet pro- 
cess a zinc plate coated with asphaltum is exposed be- 
neath a negative, and those portions unchanged by light 
are dissolved. The zinc is then etched. Photographs are 
reproduced in the form of half-tone plates for use in the 
printing-press by several methods, all of which depend 
upon breaking up the surface of the picture by dark lines 
in regular series. A gelatin film on which such a series of 
lines has been photographed is placed between the sensi- 
tized surface which is to receive the impression and a 
positive picture. The resulting print will consist of the 
subject appearing in half-tone on a ground of lines, and 
from it a typographical matrix is prepared in the usual 
Wa 7 s j (For an example of a half-tone plate, see cut under 
aekadrachm.) Also called photographic engraving, photo- 
graphic-process printing, photographic process. See photo- 
etchnui (Gillet process), and compare heliatypy and photo- 
gravure. 
photo-epinastic (fo-to-ep-i-nas'tik), a. f<pho- 
to-epinast-y + -ic.] In hot., of, pertaining to, 
or ot the nature of photo-epinasty. 
photo-epinastically (fo-to-ep-i-nas'ti-kal-i), 
cutv. In lot., in a photo-epinastic manner, 
photo-epinasty (fo-to-ep'i-nas-ti), n. [< Gr. 
0uf (<t>uT-), light, + E. epinasty.] In lot., an 
for printing like a plate. The gutta-percha plate is 
a hardened impression from a relief negative in bichro- 
mated gelatin, made according to the methods used in 
photo-process. 
photogen (fo'to-jen), n. [F. photogene, < Gr. 
(tof (0r-), light, + -yevf/c, producing: see -gen.] 
A paraffin-oil : game as kerosene. 
photogene (fo'to-jen), n. [< Gr. 0>f (<t**>T-), light, 
+ -yevfa, producing: see -gen.] A more or less 
continued impression or picture on the retina. 
H. Spencer. 
photogenic (fo-to-jen'ik), a. [= F. photoge- 
niqttti = It. fotogenico ; as photogen-, photogen- 
ous.] 1. Of or pertaining to photogeny. 2. 
In tool., producing light without sensible heat, 
as an animal or vegetable organism; giving 
rise to luminosity or phosphorescence; pho- 
togenoug. 
According to Schulze the males of Lampyris splendidula 
possess two photogenic organs. 
Huxley, Auat. Invert., p. 379. 
Photogenic drawing, (a) A picture produced by the 
agency of light, according to any of the photographic pro- 
cesses. Specifically (b) A reproduction of the configura- 
tion of any flat translucent object, as a leaf, or the wing of 
an insect, or a drawing upon translucent paper or tracing- 
cloth, made by confining it under glass in contact with a 
sensitive film, exposing to the action of light, and fixing 
or developing the image resulting in the film. A variety 
of photogenic processes are now in use for copying me- 
chanical drawings. See blue-printing. 
photogenous (fo-toj'e-nus), a. [< Gr. 0f (<M"-)> 
light, + -yevfa, producing: see-genotis.] Inbiol., 
same as photogenic. 
Their further studies . . . enable them to reconcile 
their theory of photogenous fermentation with the hypothe- 
sis of the oxidation of a phosphorated substance, as pro- 
posed by some biologists. Nature, XXXVIII. 512. 
photogeny (fo-toj'e-ni), . [< Gr. 
light, + -ytveia, < -yevfis, producing: see -geny.] 
The art of taking pictures by the action of light 
on a chemically prepared ground ; photography. 
photpglyphic (fo-to-glif 'ik), a. [< photoglyph-y 
+ -ic.] Of or relating to photoglyphy. 
photoglyphy (fo-tog'li-fi), . [< Gr. 0or ($w-), 
light, + -yUtfieiv, engrave.] The art of engrav- 
ing by means of the action of light and certain 
chemical processes; particularly, the produc- 
tion by photographic processes of a plate from 
which copies can be printed in ink. Often re- 
stricted to the production of intaglio plates, Or 
photogravure. 
photo- 
graph. Nature, XXXVI. 317. [Rare.] 
photogrammetry(f6-to-gram'et-ri), . The art 
of forming an orthogonal projection from two 
perspectives. 
photograph (fo'to-graf), n. [= F. photograplie 
= It. fotografo, a photograph (cf . Sp. fotografla 
= Pg. pliotographia = It. fotografia, a photo- 
graph: see photography); Sp. fotografo = Pg. 
photographo = It. fotografo = G. photograph 
= Sw. T) au . fotograf = NG'r. QuToypaQos, a pho- 
tographer, < Gr. ipaf (pur-), light, + Ypfyecv, 
write.] A picture produced by any process of 
photography Composite photograph. See compos- 
ite. Instantaneous photograph. See photography. 
-Phosphorescent photograph, a photographic pic- 
ture obtained by coating a plate with a mixture of dextrin, 
honey, and potassium bichromate, and exposing it under 
a negative. The parts affected by light through the trans- 
parent parts of the negative harden, while those which 
are protected from the light remain sticky, so that any 
flne powder dusted over will adhere to them, while hav- 
ing no hold on the hardened parts. If a phosphorescent 
powder is dusted on this positive, and the plate is then 
exposed to strong light, there will result a picture appear- 
ing luminous in the dark. 
photograph (fo'to-graf), v. t. [< photograph, 
n.] To produce a likeness or facsimile of by 
photographic means 
photography 
photographer (fo-tog'ra-fer), n. [(photograph 
+ -'/'.] One who makes pictures by means of 
photography. 
photographic (t'6-to-graf'ik), a. [= F. phota- 
grapMque = &p. foiogrdfico = Pg. photograph i- 
co = It. fotografico; as jilmtograph-y + -ic.] 
Of, pertaining to, using, or produced by pho- 
tography Photographic engraving. Same as photo- 
engraving. Photographic lens, paper, etc. See the 
nouns. Photographic process, photographic-pro- 
cess printing. Same nsphoto-entrraiing. 
photographical (fo-to-graf 'i-kal), a. [< jihoto- 
ijntplnc + -a/.] Of or pertaining to photogra- 
phy ; more or less directly connected with pho- 
tographic matters: as, &pliotogrphical print ; 
a photographical society. 
photographically (t'6-t'o-graf 'i-kal-i), adv. By 
means of, or as regards, photography; as in a 
holograph. 
Otographometer (f6"to-gra-fom'e-ter), n. [< 
photograph + Gr. /itrpov, measure.] 1. In 
photog., an instrument for determining the 
sensibility of a film employed in photographic 
processes, relatively to the amount of radiation, 
luminous and chemical. 2. A rotating photo- 
graphic apparatus for recording automatically 
the angular position of objects around a given 
point. 
photography (fo-tog'ra-fi), >i. [= F. photo- 
graphic = Sp. fotografia = Pg. photographia 
= It. fotografta = D. photografte = G. photo- 
rapltie = Sw. Dan. fotografi, photography (in 
p. Pg. It. also a photograph), = NGr. (toro- 
ypcujiia, photography, < Or. 0of ((tor-), light, + 
-ypafia, < ypafytiv, write. Cf. photograph.] The 
art of producing images of objects by an appli- 
cation of the chemical change produced in cer- 
tain substances, as silver chlorid, bromide, or 
iodide, by the action of light, or more gener- 
ally of radiant energy. The rays which are in gen- 
eral most active in this way are those of the upper part 
of the spectrum, as the blue, violet, and ultra-violet rays. 
Tlie red and yellow rays produce a much less marked ef- 
fect on an ordinary sensitive plate ; but it has been found 
possible to prepare a special gelatinobromide plate which 
is highly sensitive even to the less refrangible rays, as 
those in the infra-red region of the spectrum. (See spec- 
trum.) Photography rests on the fact that silver nitrate 
and various other chemicals are decomposed by certain 
solar rays and reduced, becoming dark or black, or in other 
ways affected, according to the intensity and amount of 
actinic rays received on them. The process consists (1) 
in properly exposing a surface made sensitive to actinic 
rays to a projected image of the object to be reproduced ; 
(2) in rendering visible if merely latent, or in coloring or 
toning, the reproduction of this image ; (3) in removing the 
sensibility of those parts of the surfacewhich have not been 
acted on, and in fixing permanently the image produced ; 
and (4), if the image obtained is a negative, as in the major- 
ity of processes, in the mechanical production of positive 
copies from it. The knowledge of the principle on which 
photography depends reaches back to the time of the alche- 
mists, who discovered that silver chlorid exposed to the 
sun's rays became black. Wedgwood and Davy in 1802 
attempted to apply this fact to artistic purposes by throw- 
ing the shadow of an object on a sheet of white paper, 
or, preferably, of leather, covered with a solution of silver 
nitrate and exposed to the sun's rays, but they were un- 
able to fix the pictures. About 1814 Niepce, a Frenchman, 
discovered a method of producing pictures on plates of 
copper or pewter covered with a sensitive resinous sub- 
stance called bitumen of Judea, and also of rendering them 
permanent This process he called heliography. Niepce as- 
sociated himself with Daguerre, who elaborated, about 1838, 
from the former process the one which bears his name. (See 
daguerreotype.) This was soon superseded by various pro- 
cesses, especially the calutype process (see calotype)of l*'ox- 
Talbot, first patented in 1841, who revived Wedgwood's 
process of obtaining pictures on sensitized paper, and the 
collodion process (see collodion), first suggested by M. Le 
Grey, of Paris, and brought into practice by Archer in 1850; 
and all these later processes have been practically aban- 
doned for the gelatinobromide dry-plate process, which is 
now in almost universal use. Photographs produced by 
any of these processes may be either negative or positive. 
Negative photographs exhibit the lights and shades as op- 
posite to those in nature that is, the lights appear dark 
and the shades transparent; positive photographs exhibit 
the lights and shades in accordance with nature. To pro- 
duce a positive from a negative, the latter is placed in con- 
tact with a surface which has been rendered sensitive to 
light, and is exposed to the influence of light, which pene- 
trates the negative and affects the parts of the underlying 
surface opposite the lights of the picture, while the parts 
opposite the opaque parts of the picture are protected. The 
operation for obtaining a positive from a negative is called 
printing. Modifications are constantly being introduced 
in photography. One of the most important has been the 
carbon process, popularized by Swan of Newcastle, accord- 
ing to which a solution of gelatin and potassium bichromate 
(the latter being the sensitizing agent) is mixed with a 
pigment, and applied as a coating to a sheet of paper. The 
positives are printed in the ordinary way on the black 
cake, or tissue as it is called, thus produced, and become 
visible and permanent by washing, as the pigment-coating 
is rendered more or less insoluble by the effect of the light 
passing through the negative. The autotype process, in- 
vented by Johnson, is a simpler method of carbon-print- 
ing than the carbon process proper, but the principles in- 
volved are the same. One of the most important devel- 
opments of the art is the so-called AuCMfBfM0Vf photog- 
raph)/, by means of which, through the use of very sensi- 
tive plates and the shortness of the duration of exposure, 
