PHOTOPHONE 



PHOTOSPHERf 



are mounted on opposite sides of 

 the screen, and their distances 

 adjusted so that the grease spot is 

 invisible : the intensities of the 

 two lights are to one another as the 

 squares of their distances from the 

 screen. In a Rumford photometer 

 a vertical rod is mounted in front 

 of a screen, and the positions of the 

 sources of light are so adjusted 

 that the two shadows which they 

 cast are substantially equal. For 

 determining the intensity of a 

 bright light, such as an electric 

 arc, a dispersion photometer may 

 be used. The dispersive effect of a 

 thin concave lens acts, as the in- 

 creased distance in the common 

 photometer, to reduce the intensity 

 of the light to the required degree. 

 Polarisation, wedge, wheel, and 

 other photometers are also well 

 known. 



Photophone (Gr. phos, light; 

 phone, voice). Instrument for 

 transmitting sounds by means of 

 light. The instrument depends 

 upon the varying electrical re- 

 sistances of selenium under the 

 action of light. In its essentials a 

 beam of light falls upon a thin, 

 flexible mirror which forms a dia- 

 phragm similar to that of a tele- 

 phone. The reflected light from the 

 mirror passes through a lens, and 

 thence to another receiving mirror, 

 which concentrates it on a selenium 

 cell connected with an electric 

 batter}' and telephone. The vibra- 

 tion of the first mirror, due to 

 speech or other sound, scatters the 

 light and sends intermittent rays 

 through the lens, and so to the 

 selenium cell. The variation of 

 light on the selenium provides the 

 variation of electric resistance, 

 which enables correspondingsounds 

 to be heard in the receiving tele- 

 phone. Lampblack has been sub- 

 stituted for selenium (q.v.). 



Photo-Sculpture. Process by 

 which it is possible to photograph 

 a person or object in such a way 



that from that photograph a 

 carving, in relief or intaglio, can be 

 made in ivory, alabaster, wood, or 

 other hard material. The inventor 

 was H. M. Ediuunds, of Brighton. 

 The apparatus consists, in the 

 first place, of an optical projector 

 (magic lantern) with a long focus 

 and well-corrected lens, illuminated 

 by an incandescent lamp of high 

 candle power. The lantern slide 

 is a " spiral " photograph on plate 

 glass, the " spiral " being accur- 

 ately drawn in a form like that of 

 the groove of a gramophone re- 

 cord. This spiral is focused upon 

 a plain surface at 9 or 10 ft. from 

 the projector lens. To the 

 side of the projector is fixed 



Photophone. Dia- 

 gram illustrating 

 principle of the in- 

 strument. A. Lens 

 concentrating light on silvered glass 

 mirror, B, which forms part of re- 

 ceiver, C. D. Lens directing re- 

 flected light from mirror on parabolic 

 reflector, E, which concentrates light 

 received on selenium cell, F, attached 

 to a telephone receiver by connexion, g. 

 h. Mouthpiece 



Photo-Sculpture. Carving machine with which the 

 operator, bis eye at the microscope, follows the lines on 

 the photo, and simultaneously operates the drill on the 

 material affixed to the face-plate on the light. Top, 

 right, spiral photograph of the inventor. See text 



a camera in such a 

 way that the opti- 

 cal axes of the pro- 

 jector and camera 

 lenses are parallel. 

 The spiral pro- 

 jected on the plane 

 surface is then pho- 

 tographed in the 

 ordinary way, the 

 negative obtained 

 is enlarged on an 

 opal glass, and the 

 resulting record is 

 then placed on a 

 moving carrier that 

 forms part of the 



" carving machine " ; the other two 

 main elements of this machine 

 Leing (1) a face-plate, which holds 

 the material to be carved, and (2) a 

 high-speed drill and microscope 

 mounted up together, which can 

 be moved by a controlling lever. 

 The movement of the carrier of the 

 photographic record is mechanically 

 connected with the movement of 

 the material to be carved, so that 

 the one corresponds exactly to the 

 other when the lever is operated. 

 The operator, with his eye pressed 

 to the upper end of the microscope, 

 merely has to follow the lines, 

 enlarged by this instrument, which 

 are indicated on the photo- 

 graph, moving the micro- 

 f scope to do this with the 

 controlling lever. The drill 

 is moved at the 

 same time as the 

 microscope, so that 

 it cuts the material 

 at varying depths 

 according to the 

 form of the original object, and the 

 relief or intaglio is evolved. 



In regard to material, the best 

 results have been obtained in ala- 

 baster by the inventor, but various 

 woods and ivory have also proved 

 very adaptable. Any number of 

 sculptured copies required can be 

 made from the single photographic 

 record. 



Photosphere. In astronomy, 

 the visible surface of the sun. The 

 main body of the sun consists of 

 gases under enormous pressures. 

 On the surfaces these gases become 

 highly incandescent, and give a 

 continuous spectrum. That part of 

 the surface is the photosphere ; 

 above it is another gaseous en- 

 velope, the chromosphere. The 

 photosphere has the appearance of 

 snowflakes which are beginning to 

 cover a dark background. Large 

 breaks appear in the photosphere, 

 the so-called sun-spots, first no- 

 ticed by Fabricius in 1610. These 

 spots vary in size, trom a few hun- 

 dred miles across to huge chasms 

 thousands of miles wide, and some- 

 times last many months. In the 

 neighbourhood of many of the sun- 

 spots there often appear bright 

 streaks or patches in the photo- 

 sphere. These bright streaks are 

 known by the name of faculae, 

 or little torches. They arc more 

 distinctly seen near the edge of the 

 sun, where the general brightness 

 of the surface is lessened by the 

 greater thickness of the absorbing 

 atmosphere. The photosphere 

 does not revolve evenly, the lower 

 latitudes moving faster than the 

 higher, a fact established by obser- 

 vation of the time taken by the spots 

 to travel across the face of the sun. 

 The general appearance is mottled 



