PHOTOMETER 



Photo-Lithography. Machine for multiplying a de- 

 sign from original negative on to a larger negative. 

 A. Lens. B. Lantern containing original negative in 

 frame C. D, E. Dials controlling movements of 

 multi negative G. H. Wheel regulating size of pro- 

 jected image. J. Printed sheets. See text 



plate after each exposure, so that 

 each set is not a secondary impres- 

 sion as in the case of hand trans- 

 ferring. Thus, there may be six 

 large machine plates with the six 

 colours all in perfect register, each 

 having its own original 16 or 32 

 times as required. So efficiently 

 does this method fulfil all require- 

 ments of colour registration, that 

 the delicate levers in conjunction 

 with dials move the large machine 

 plate vertically and horizontally 

 to within a thousandth part of an 

 inch. Afterwards the exposed 

 plate is rolled with ink, when the 

 image clearly appears and the 

 multi plate is then ready for the 

 printing machine. 



An alternative method of dupli- 

 cation is by a repeating camera 

 or projector like a cinema lantern, 

 which repeats a subject from the 

 master negative on to a larger one 

 as many times as desired, i.e. 

 instead of duplicating from the 

 negative on to a machine plate 

 direct, it repeats the negative 

 photographically, one original of 

 one subject 16 or 32 times or 

 more on to another nega 

 tive all in register. Thus 

 a large multi nega- 

 tive with 16 or 

 32 set thereon is 

 obtained, which is sub- 

 stituted for the single nega- 

 tive. This latter device is used 

 largely for repeating on printing 



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plates, postage 

 stamps, small labels, 

 and paper script 

 where large quanti- 

 ties are required. 



A multi negative 

 having been ob- 

 tained, the next 

 procedure is to 

 transfer the subjects 

 thereon to the print- 

 ing machine plate en 

 bloc ; the machine 

 plate, having been 

 sensitised, is fitted 

 into a printing-down 

 frame and the multi 

 negative placed 

 upon the top of it. 

 Close contact be- 

 tween negative and 

 plate is ensured by 

 the extraction of all 

 air, and it is then ex- 

 posed to a powerful 

 light. The machine 

 plate is now taken 

 from the frame and 

 rolled with ink, 

 which adheres to the 

 images secured from 

 the multi negative 

 by the exposure. 



When a subject 

 is to be printed 



respectively (1) offset, (2) direct, 

 the subject on the machine plate 

 has to be (1) the same view optic- 

 ally as the original painting instead 

 of reversed as in the case of (2) 

 direct printing, and the cycle of the 

 photographic operations is pro- 

 vided for beforehand accordingly. 



The machine plates made by 

 either of these two distinct photo- 

 graphic methods of duplication, 

 i.e. (1) from the single negative 

 direct to the machine plate, (2) by 

 means of a multi negative, have a 

 life, value, and sharpness of detail 

 not possessed by the older methods. 



The machine plates produced by 

 any of the methods, described are 

 next fitted into the printing machine 

 and copies pro- 

 duced in bulk 

 either direct or 

 offset from a reel 

 of paper or 

 from flat 

 sheets. 



Photometer. 

 Diagram of 

 Rumford type. 

 A. Screen. B. Rod 

 throwing shadow on 

 screen. C. Standard 

 light candle. D. Lamp to be 

 compared with candle, c. 

 Shadow thrown by candle, d. Shadow 

 thrown by lamp. EE'. Measuring scales 



PHOTOMETER 



With the advent of the offset 

 principle of printing off and a 

 better adaptation of photography 

 the whole cycle of lithographic 

 printing is in a further state of 

 evolution endeavouring to outstrip 

 its older companion typography, 

 and to keep pace with its newer 

 rival photogravure. The introduc- 

 tion of photo-lithography used in 

 conjunction with offset machining 

 has given it a new lease of life, and 

 extended its possibilities so greatly 

 that much of the work which has 

 hitherto been done by letterpress 

 printing can be done equally well, 

 if not better, by lithography, and at 

 a lower cost. The excellence of the 

 combined process can be seen in 

 most art depots, where there are 

 prints so like the originals as to be 

 easily mistaken for them ; to some 

 extent letterpress relief illustrations 

 supplanted lithography, and the 

 latter is now getting its revenge with 

 the aid of photographic science. 



Attempts are being made to 

 print newspapers by photo-litho- 

 graphy with some measure of 

 success, and if by this process 

 costly stereotypes can be dispensed 

 with its economic value will be 

 apparent. The outstanding diffi- 

 culty of securing a lithographic 

 plate with a long life, and from 

 which a vast number of newspaper 

 impressions can be printed at a 

 very high speed, is being overcome 

 by a hardening process. 



When a planographic plate fulfils 

 the requirements of the printer in 

 the directions referred to, having 

 regard to the economy effected, 

 both in time and cost, the stereo- 

 type will, it is predicted, become 

 as obsolete as the woodcut for 

 newspaper production. 



Photometer (Gr. photos, of 

 light; metron, measure). Instru- 

 ment for measuring the actual 

 intensities of light, usually against 

 some standard source. The stand- 

 ard in use in Great Britain is the 

 candle power, the light produced 

 by a sperm candle one-sixth of a 

 pound in weight and burning 120 

 grains of wax to the hour. Such a 

 standard is unsatisfactory, because 

 of the difficulty of obtaining uni- 

 formity in the composition of the 

 wax and a wick that will burn 

 uniformly. The Carcel lamp, the 

 French standard, burns colza oil 

 at a fixed rate, and is more satis- 

 factory. Other standard sources of 

 light which have been proposed are 

 that given out by a square centi- 

 metre of melted platinum, that 

 from a square millimetre of a pure 

 carbon arc, the acetate of amyl 

 lamp of Hefner, etc. 



In a Bunsen photometer a white 

 screen has a grease spot at its 

 centre. The lights to be compared 



