56 



KNOWLEDGE & SCIENTIFIC NEWS. 



[April, 1904. 



made to Darwin — for his observations and disco\eries 

 in tile Palaeozoic series of roclvs, and more especially for 

 his determination of the characters of the Devonian 

 system. Other honours were showered upon him, both 

 at home and from abroad, including, in the former 

 category, the Presidency of the Geological Society and 

 of the British Association. 



As a contemporary of L)ar\vin, Professor Sedgwick 

 was confronted with that naturalist's theory respecting 

 the evolutionary order of Nature. His attitude was uni- 

 formly hostile to the hypothesis, and he would have 

 none of it. In this connection it is interesting to note 

 that, at the time of the publication of the " Origin of 

 Species," Darwin was exceedingly sore at the " rabid 

 indignation " displayed by Sedgwick, nevertheless he took 

 occasion to refer in affectionate strain to the veteran 

 geologist's noble heart and instincts. 



Sedgwick never married. He continued his occupancy 

 of the professorial chair until his death, in i>^73, which 

 took place at the ripe age of eighty-eight, and he was 

 buried in the ante-chapel of Trinity College. 



Finally, let these words of his further proclaim the 

 man : " My labour is its own reward. It gave me health, 

 and led me into scenes of grandeur which taught me to 

 feel in my heart that I was among the works of the great 

 Creator." 



Telegraphically Trans- 

 mitted PhotogrsLphs. 



By Dr. Alfred Grauenw it/. 



Many attempts ha\e been made to transmit handwriting, 

 photographs, drawings, (S;c.. by telegraphic means, and the 

 more or less successful solutions which have been suggested 

 for this problem of late years are numerous. Selenium cells, as 

 shown by Herr Ruhmer's successful experiments in the field 

 of wireless telephony, give a ready means of detecting and 

 transmitting by telephone even very slight fluctuations in the 

 intensity of a source of illumination, and afford means ol con- 

 verting these fluctuations into oscillations of an electric current. 

 If a hght ray and a selenium cell be simultaneously drawn 

 along over opposite sides of a photographic plate, llie different 

 shades of the various portions of the plate will result in con- 

 tinuous oscillations of the current being produced in the cir- 

 cuit of the cell This is a common feature with all the sending 

 devices used in the instruments of this class. The current 

 oscillations are made to act on the receiving apparatus, which 

 will reconvert them in turn into fluctuations of light. The 

 design of the receiving apparatus has hitherto been the weak 

 point with all these systems, because the electric currents 

 transmitted are so Aery small. Hut a satisfactory solution of 

 the difficulties so far met with seems to be aflorded 

 apparatus of I'rofessor Arthur Korn. 

 presented before the French Academy 



by the teleoptical 

 ^Iunich, as recent! v 

 of Sciences. 



While engaged in investigating the radiations given off by 

 the electrodes of a tube exhausted to a pressure ranging be- 

 tween 0-2 and 2 mill, as Hertzian vibrations were applied to 

 the electrodes. Professor Korn noticed the extreme seubitive- 

 ness with which these radiations would react on small altera- 

 tions in the circuit. This sensitiveness suggested a possible 

 utilisation of those radiations which were photographically 

 most efficient, in connection with a method of electrical tele- 

 photography. 



The apparatus, based on the above principle, is shown in 

 fig. 1. 



The photographic film a uf the receiver rotates in front of a 

 small window c (0-25 mm x 0-25 mm) in an exhausted tube /), 

 like a roller, in front of the \ibratiug membrane ot a phono- 



graph. The surface of the tube is coated with black paper 

 and tin-toil, lea-i-ing only the window. By means of high fre- 

 quency currents (Tesla currents), luminous radiations may be 

 produced inside the tube, and these, after passing through the 

 small window, will make photographic impressions on the sen- 

 sitive film. The latter is moved synchronously with the image- 

 holder A of thesending-apparatus(afilm bearing the photograph 

 to be transmitted wound on a glass cylinder), which is traversed 

 by a very thin beam of light B C D while passing, line per line, 

 before a selenium cell D placed inside the cylinder. .According 

 to the different shades in the photograph transmitted, thesele- 



SoKlif of 



Light 



'SjjtA I 



Gxj^^acciXXf 



Fig. 



nium will receive more or less light, while an electric current, 

 passing through the selenium D and the telegraphic wire F up 

 to the recei\'ing apparatus, will undergo corresponding varia- 

 tions of intensity, thereby regulating the intensity of the 

 radiations of the receiving tube. This is provided for in the 

 following way: The active electrode e of the tube being con- 

 nected to one of the poles />, of the secondary coil of a Tesla 

 apparatus, by inserting fields of sparks formed by the points 



Original Photograph. 



Transmitted Photograph. ^ .» 



nil, uij, of a galvaifometer needle / and two fixed points", fj, L, 

 the intensity of the radiations given off by the tube will be 

 more or less great, according to the distances nij fj and m, 

 and (2, which are variable along w-ith the transmitted currents 

 passing through the galvanometer i'. By the use of this 

 arrangement, a means is afforded of making the intensity of 

 the radiations of the receiving tube correspond with the in- 

 tensity of the light striking the selenium of the sending- 

 apparatus, thus reproducing line per line of the original photo- 

 graph. 



