FIRST RESEARCHES IN PHYSICS 57 



filings have thus acted, a tap suffices to shake them back to 

 their former irregularity, and the apparatus is ready for 

 the next experiment. 



Lodge made able use of this simple expedient ; he also 

 offered an interpretation of its action, as due to. fusing or 

 soldering of the minute points of contact of the filings 

 by the inductive effect produced in them through the 

 incidence of the Hertzian waves, and for this reason he 

 renamed it a 'Coherer/ Branly, however, maintains the 

 original name, with his explanation that the Hertzian 

 waves merely modify in some ways the non-conducting 

 film upon the surface of the filings. Bose's receiver a 

 great advance on that of Branly and Lodge, of which the 

 sensibility is variable, sometimes even seeming capricious- 

 replaced the irregular filings by fine wire spiral springs, 

 adjusted with a thousand regular contacts or thereabouts, 

 and fixed in ebonite, and under control by a screw, A weak 

 current is passed through this, to which the spirals offer 

 a very appreciable resistance. The current is enormously 

 reduced, as with Branly's apparatus, but now even more 

 sensitively and more regularly when the instrument is 

 placed in the path of the electric waves ; the more since 

 the electric beam of Bose's generator is not only sharp and 

 well defined, but better regulated. The sensibility of 

 this apparatus, says M. Poincare (to whose clear treatise 

 the writer' is much indebted), f is exquisite: it responds 

 to all the radiations in the interval of an octave. One 

 makes it sensitive to different kinds of radiations, by vary- 

 ing the electromotive force which engenders the current 

 which traverses the receiver.' Bose also was successful in 

 inventing other types of receivers which recovered auto- 

 matically without any tapping. It is also well worth notice 

 that the whole apparatus has thus not only been Improved 

 by Bose and perfected in all details, but condensed from 

 the enormous dimensions of Hertz's original devices, and 

 -the still very considerable magnitude of those of Lodge and 

 other investigators, to a small and compact set of .appliances, 



