photography 
scenes, motions, etc.. are p-pro-lnred and registered whieb 
ure too rapid or eranMOttottobediitingiiiihiblabytbeeye. 
For various mechanical methods of multiplying photo 
graphic piet III. -s, si -e/J/IMo-i ,l,,'lK,l,l l ,',lll,"ln ' n'lf'l rillfl, /.I, :, 
phy, und lit'li"l>/iiii. 
photogravure (fo'to-gra-viir'), . [< F. ;;///- 
t/rai'iirt; ir. pwf (0<jr-), light, + K. tint run; en- 
graving. ] The arl ol 1 priHlneing on metal, by 
an application of the action of light on u sensi- 
tized surface, often sn]ii)lementeil liy etching, 
an incise. I engraved plate for print in";, iio-,, 
are several processes by which this may be aerornpli>h' M. 
According to the Niepee process, which Is suitable for the 
reproduction of line-enKl'avillfJs, a eopperplali K coated 
witll bitumen :ind is then exposed to light beneath a ncg 
alive. The resulting print is brought, out with olive-oil 
and turpentine, or with oil of spike, which dissolves the 
parts acted on by light and acts little on the rest, and the 
lines remain as bare copper. The plate Is then eteb- d. 
In the i o\ Talbot process the gelatin print Is transferred 
to copper which has had a grain given to it by sprink- 
ling the surface with powdered resin and then warming 
It. 0MflnMflMO The plate is then etched witli ferric 
acid, which renders the opaque portions of the gelatin 
Him insoluble and impermeable. The acid should In- 
weak and kept in motion during the biting, until the un- 
covered parts have been sutnciently attacked. To inen-.iM 
the regularity of the erosion, the plate should first be Im- 
mersed in a weak solution of copper sulphate. In the 
Woodbury process, which resembles the (Jotipil process, a 
gelatin picture in relief is applied under pressure upon a 
plate of soft metal, and Is repeated on the metal in relief 
and depression. The mold thus formed is tilled with pig- 
menteu gelatin, over which a sheet of paper which is to 
receive the picture is placed, and subjected to a level 
Sressure in order to force out the superfluous gelatin. The 
epressed parts, which represent the dark parts of the 
picture, retain the most gelatin, and when the paper is 
lifted it raises the gelatin from the mold in such a manner 
that it forms a picture in low relief. In order to obtain 
a grained surface which will hold printing-ink, pounded 
glass may be mixed with the gelatin. 
photogravure (fo'to-gra-vur'), v. t.; pret. 
and yp.photogravurea, ppr. photogravuring. [< 
photoi/rui'iirc, n.] To produce in photogra- 
vure. 
photoheliograph (fo-to-he'li-o-graf), n. [< Gr. 
0<if (0ur-), light, + E. heliograph.] A photo- 
graphic telescope designed for making photo- 
graphs of the sun, particularly at a transit of 
Venus or at a solar eclipse. There are several 
forms of the instrument, differing widely in con- 
struction. 
photoheliographic (f6-to-he"li-o-graf'ik), a. 
[< photolit'/iiii/i'iiiili + -ic.] Of, pertaining to, 
or made by means of a photoheliograph : as, 
nhotolit'/iot i ni />liic observations. 
photohyponastic (fo-to-hi-po-nas'tik), . [< 
liliiitolii/puntixl-y + -ic.] In bot., pertaining to 
or characteristic of photohyponasty. 
photohyponasty (fo-to-hi'po-nas-ti), n. [NL., 
< Gr. ^<Jf (<t*jr-), light, + E. kj/pOHOtty.] In 
bot., a hypouastic movement or curvature 
brought about by the exposure of organs to in- 
tense light after they have had their growth 
arrested for a period. 
photolithograph (fo-to-lith'o-graf), n. [< Gr. 
</xl>i; (tfxjT'), light, + E. lithograph.] A print 
produced by photolithography. 
photolithograph (fo-to -lith 'o-graf), v. t. [< 
liliiittilit/iiitp'ii/ilt, n.] To produce or reproduce 
by the aid of photolithography. 
photolithographer (fo'to-li-thog'ra-fer), n. [< 
pkototttkogrmn-g + -re 1 .] One who produces 
pictures by photolithography. 
photolithographic (fo-to-lith-6-graf 'ik), a. [< 
phototttkograph-y + -ic.] Of, pertaining to, 
or produced by photolithography Photolitho- 
graphic process, any one of the various processes by 
which photolithography is accomplished. All depend 
upi in the property of a gelatin nlm, sensitized with potas- 
sium biriironi:ite or an analogous chemical, of becoming 
insoluble when exposed to light, and thus of affording a 
photographic relief-plate, or a plate which will take litho- 
graphic ink in the parts affected by light, and repel it else- 
where, from which the design orplcture can be transferred 
by the ordinary methods of lithography to a stone, or to a 
plate of zinc, etc. 
photolithography (f6"to-li-thog'ra-fi),n. [=F. : 
l>hotolitlitii/rn/iliif = Sp'. fiiti>/it<ii/i-iifiit ; as Gr. J 
^uf (0wr-) + E. litliiM/rii/iliy.'] The art of fixing 
on the surface of a lithographic stone by the 
agency of the action of light upon bichromated 
gelatin combined with albumen, and by other 
manipulations, an image suitable for reproduc- 
tion in ink by impression in the manner of an 
ordinary lithograph; also extended to include 
processes of similar character in which the trans- 
fer is not made to stone ; specifically, the pro- 
cess of reproducing in ink any design or picture 
executed on prepared stone by means of pho- 
tography, either directly or by transfers from 
photographs. The process is analogous to several pho- 
to-engraving processes executed on metal. See phutnllthn- 
photologic (fo-to-loj'ik), a. {= 
= Sp.nMogieo = I'g. /;/ico/v/iV , as /iii 
+ -it:] Of or pertaining to photology. 
photological (fo-to-loj'i-kal), a. [< 
+ -til.] Same as /il/tntiMii<: 
' 
photologist (t'o-tol'o-jist), . [< pku 
-i.--t. ] < )ne who devotes himself to the study or 
exposition of the science of light. 
The painter should never forget that bis notion of colour 
(as compared with that of the photnlnyint) Is a negative oue. 
'Henchel, Light, f 48. 
photology (fo-tol'o-ji), n. [= K. iiliiiliiloijie = 
Sp. j'nliili>!f(a' = I'g! pliiitiilni/iii, < Gr. tfuf (fur-), 
light, + -Aoj'/a, < Mytiv, speak: eee-oloffy. Cf. 
MI Jr. funUytf, announcing light.] The science 
of light. 
photolysis (fo-tol'i-sis), w. [NL., < Or. <fa 
(0ur-), light, + ArfTir-, a loosing, setting free, < 
Ai'eiv, loosen, unbind, unfasten.] In hot., the 
movements of protoplasm under the influence 
of light: distinguished as /ir)W;-i/i/i and epix- 
trttjihe. In the first the chlorophyl-gralns collect upon 
the cell-walls which are parallel to the plane of Incident 
light ; In the latter, upon those which are at right angles 
to it. Moore. 
photomagnetism (fo-to-mag'net-izm), . [< 
Gr. 0<j (0ur-), light, + E. intii/n i-tixm.] The 
relation of magnetism to light. />////. 
photomechanical (fo'to-me-kan'i-kal), a. [< 
Gr. <t>&; (00T-), light, + E. nn< liiinifiil.'\ Pertain- 
ing to or consisting in the mechanical produc- 
tion of pictures by the aid of light, as in photo- 
engraving, photolithography, etc. 
Of all the perfected photomechanical processes, the col- 
lotype is about the most useful for general purposes. 
The Engine, LXVI. 279. 
photometallograph (to'to-me-tal'd-graf), n. 
[< Gr. <j>uf (fur-), light, H- utraUnv, metal, + 
ypcujietv, write (see metallograjihy).] Same as 
photozincograph. 
photometer (fo-tom'e-ter), n. [= F. photomitre 
= Sp. fotomctro = Pg. photometro = It. fotimti-- 
tro, < Gr. <t>uf (0wr-), light, + fiirpov, measure.] 
An instrument used to measure the intensity 
of light, specifically to compare the relative 
intensities of the light emitted from different 
sources. Many forms have been devised, most of which 
are based upon the determination of the relative distances 
photophone 
tinted dark glass is used to cm- M,. apparent e\tjnetion 
of a st;ir \iewed ihiom-h it. The tlii.-kn.-ss of II. . we.lg.' 
at the point where the star vanishes il>-t. unities its bright 
ness. Wheel photometer, an m-minn nt in uliich the 
li^'bt to be nieaMiM if in any required degree 
by transmission through adjustable :ipeiliucH in a rapidly 
revolving wheel. 
photometric (fft-ty-mefrik), . [= F. />///- 
Hirtrii/ui' = !'(,'. iiliiiliniii Ii ifn : :i- jili'it'tim tr-y + 
-.] Pertaining to photometry, or t lie mea.-iiie- 
inent of the intensity of light, or lo the photom- 
eter, or instrument liy which this is effected; 
employing or made by a photometer; us, />ln>- 
tti in' t rif rcM-ardies nr nlisei-va lions. Lambert's 
photometric law (named after Johann Hcinrich Lam- 
bert (1728-77), an eminent matin matleian and logician, 
the discoverer of this law], the fact that a smooth, irregu- 
larly reflecting surface appears equally in i'-'M under what- 
ever angle it is seen. Photometric standard, a carcel 
lamp burning 42 grains of refined colza-oil JMT hour, with 
a flame 4o millimeters high. It is equal to H.. I'.i m-h or 
7.6 Gennan standard candles. The unit <-i 
. . 
adopted by the Electrical Congress at Paris (1884) Is the 
amount of light emitted from a surface of one square 
centimeter of melted platinum at its temper at in e ot -olid 
ificatfon; in tH89 one twentieth of this unit was adoptexl 
as the practical unit, and called a candle. See caitillr- 
photometrical (fo-to-met'ri-kiil). u. 
iiii i fif + -nl.] Same as photwnetric. 
photometrically (fo-to-met'ri-kal-i), adv. As 
regards photometry; by meansof u photometer. 
photometrician (fo'to-me-trish'an), w. [< pho- 
tometric -t- -KIM.] One who is versed in pho- 
tometry. B. A. Proctor, The Sun, p. 302. 
photometrist (fo-tom'e-trist), n. [<photome- 
tr-y + -int.] A photometrician. 
The best way for a phtitoinetrut to be certain of his In- 
struments Is to test them himself. 
W. R. Bmctlilch, Coal tias, III. 67. 
photometry (fo-tom'et-ri), n. [= F. photome- 
tric = 8p. fotvmetria = It. fotometria, < Gr. df 
(fur-), light, + -/lerpia, < /ttrpov, measure.] The 
measurement of the relative amounts of light 
emitted by different sources. This is usually ac- 
complished by determining the relative distances at which 
two sources of light produce equal Intensities of Illumi- 
nation. See phntometer. 
photomicrograph (fo-to-mi'kro-graf). n. [< Gr. 
0jf (^wr-), light, + E". micrograph.] An en- 
larged or macroscopic photograph of a micro- 
scopic object ; an enlarged photograph. Com- 
pare mirruphotograph. 
photomicrographer (f6*to-mi-krog'rii-fer), n. 
[(.photomicrograph + -cr 1 .] A maker of pho- 
tomicrographs ; one who enlarges photographs, 
or makes enlarged pictures of small or micro- 
scopic objects. 
photomicrographic (fo-to-mi-kro-graf'ik), a. 
[< photomicrograph-y + -c.] Of, pertaining to, 
or used in photomicrography; obtained or made 
by photomicrography: as, photomicrographic 
apparatus; a photomicrographic representation. 
bkl 
ngraving p 
graphicpriKcss, under phntulithoyraphif. Also called litlm- 
photofjraphy. 
Bunsen's Photometer. 
a, balance by which weight of candles burned in a given time is de- 
termined : , candles; g, clock, and meter which measures the gas 
consumed in the test ; /, gas-burner ; A, flexible pipes for supplying 
gas to the burner; if, rjfirnMxn, supported on a carriage J/ t. scale 
having a guide-way for the carriage of the sight-box, and graduated 
to show the relative candle-power of gas which gives an illumination 
having intensity equal to that of the candles. This graduation cor- 
responds with the position of the sight-lmx when the Utter is adjusted 
so that equal intensity is obtained on Itoth sides of the disk ; f is a cur- 
tain to exclude other light during the adjustment of the sight-box ; f, 
cord running over pulleys under the buttom of the instrument, by 
which an operator can start or stop the clock at the beginning and 
endof the test ; *, disk, with the translucent serrated spot? ; m, sight- 
tube; off', mirrors. Light enten the sight-box from the camtles 
through the opening y in the side of the sight-box, and from the gas- 
burner on the side of it. Images of both sides of the illuminated disk 
are simultaneously seen at H T>y reflection from the mirrors at o and a . 
at which the light from two sources produces equal inten- 
sities of illumination. One of the most common photom- 
eters is that of Bunsen, which consists of a screen of white 
paper with a grease-spot in its center. The lights to be 
compared are placed on opposite sides of this screen, and 
their distances are so adjusted that the grease-spot ap- 
pears neither brighter nor darker than the rest of the pa- 
per, from whichever side it is viewed. When the distances 
nave not been correctly adjusted, the grease-spot will 
appear darker than the rest of the paper when viewed 
from the side on which the illumination Is most Intense, 
and lighter than the rest of the paper when viewed from 
the other side. The intensities of the two lights are to one 
another as the squares of the distances from the screen at 
which they must be placed in order that the grease-spot 
may appear neither brighter nor darker than the rest of 
the paper. Another form is Rumford's photometer, which 
employs a screen in front of which is placed a vertical 
rod ; the positions of the sources of light are so adjusted 
that the two shadows which they cast are sensibly equal. 
-Dispersion photometer, a form of photometer by 
means of which the intensity of a brilliant light, as that 
of an electric arc, may be determined. The dispersive 
effect of a thin concave lens acts like increase of distance 
In the common photometer to weaken the bright, light to 
the required degree. Polarization photometer, an in- 
strument in which the measurement depends upon the 
properties of polarized light. Wedge photometer, an 
astronomical photometer in which a wedge of neutral- 
larging minute objects by means of the micro- 
scope, and reproducing the enlarged image by 
photography. It is to be distinguished from 
microphotography. 
photonephograph (fo-to-nef 'o-graf ), n. [< Gr. 
tjiaf (tpur-), fight, + vf^of, a cloud, + j-pd^t/v, 
write.] A name given by Abney to an ap- 
paratus for taking simultaneous photographs 
of a cloud from two points on the earth, it con- 
sists essentially of twin cameras, adjustable at any angle 
of elevation and azimuth, and, as used at Kew, England, 
placed 200 yards apart. Two sets of photographs are taken 
simultaneously at an interval of about a minute, and from 
these the heights and motions of the clouds are deduced. 
photonephoscope (fo-to-nef'o-sk6p), w. [< Gr. 
tfujf ($<JT-), light, T vftpos, a cloud, + aiurireiv, 
view.] Same as pltotntiephograph. 
photonosos, photonosus (fo-ton'o-sos, -sus), n. 
[NL., < Gr. Quc, (0ur-), light, + vAanf, disease.] 
Any affection resulting from exposure to a glare 
of light, as snow-blindness. 
photopapyrography (fo-to-pap-i-rog'ra-fi), n. 
[< Gr. ^t>f ($<JT-), light, -f- 15. papyrography.] 
A photo-engraving process in which a relief- 
print on paper is formed as a matrix from which 
prints in ink can be struck off. 
photophobia (fo-to-fo'bi-a), n. [= F. photo- 
phob\e = It. fotofonia, < N L. photophobia. < Gr. 
^if (0w-), light, + -^o/3/a, < ^o/?or, fear.] An 
intolerance or dread of light. 
photpphobic (fo-to-fo'bik), a. [< photophobia 
+ -ic!j Affected with photophobia; dreading 
or intolerant of light ; unable to bear light. 
photophone (fo'to-fon), . [< Gr. ?<if (0ur-), 
light, + tfrjvy, sound, voice : see phontl.] An 
instrument by which a beam of light may be 
made to transmit spoken words to a distance. 
