198 



ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1908. 



The two styles thus work synchronously. If now we so devise our 

 ajDparatus that when a reaches a black portion of its image, the 

 style, 5, marks upon B a black trace, then, when sufficient time has 

 elapsed for the style to have run over the entire image, we will have 

 in B a reproduction of A, except that the latter will consist of a 

 series of points and parallel traces, and so will not have the con- 

 tinuity of the original image. 



The ever-increasing use of the processes of photo-engraving has 

 accustomed us to such discontinuities and, provided the parallel traces 

 are not too far apart, experience has show^n that the reproduction Avill 

 be very satisfactory. 



Let us consider the methods used to produce the synchronism. The 

 phototelegraphic apparatus for which the processes have been the 

 most developed in this respect make use of an early conception used 

 by d'Arlincourt and which has now been carried to a very high point 

 of precision in certain actual telegraphs such as that of Baudot. 

 The device used is as follows: The sheets, A and B, are rolled upon 



rotating cylinders. The cylin- 

 der of the receiver, B, turns 

 a little faster than that of A, 

 but the advance made each 

 turn is too small to produce 

 a sensible distortion of the 

 image. In order to perfect 

 the synchronism, it is sufficient 

 to stop the cylinder, B, a very 

 short time until the cylinder. A, turns to the corresponding position. 

 At that moment a contact, controlled by A, sends through the line con- 

 necting the two stations a current, freeing B, and the two cylinders 

 start simultaneously from the corresponding parts at each turn. This 

 device avoids the accumulation of small errors in the speeds of 

 the two cylinders, and the resulting image is practically satisfactory. 

 The speed of rotation of B is so adjusted as to be a half or one per 

 cent faster than that of A and the moment of correction is so chosen 

 that it always falls somewhere on the margin of the paper where no 

 part of the picture is to fall. 



The styles marking on the cylinders would always trace the same 

 circumference if they were not made to advance gradually toward 

 one side. This movement is impressed by means of a screw parallel 

 to and whose motion is controlled by the cylinder. A nut mounted 

 on the screw carries the style and as this nut is kept from turning, 

 the style must advance. The combination of these two movements, 

 the rotation of the cylinder and the advance of the style, causes this 

 style to explore successively all points of the picture. 



Fig. 1. 



