PRODUCTION OF SOUND BY RADIANT ENERGY. 187 



this hypothesis pointed toward success. A beam of sunlight was 

 focused into one end of an open tube, the ear being placed at the 

 other end. Upon interrupting the beam, a clear, musical tone was 

 heard, the pitch of which depended upon the frequency of the interrup- 

 tion of the light and the loudness upon the material composing the tube. 



At this stage our experiments were interrupted, as circumstances 

 called me to Europe. 



While in Paris a new form of the experiment occurred to my mind, 

 which would not only enable us to investigate the sounds produced by 

 masses, but would also permit us to test the more general proposition 

 that sonoroitsness, under the iiijlue7ice of internniUent light, is a prop- 

 erty commo7i to all matter. 



The substance to be tested was to be placed in the interior of a 

 transparent vessel, made of some material which (like glass) is trans- 

 parent to light, but practically opaque to sound. 



Under such circumstances the light could get in, but the sound 

 produced by the vibration of the substance could not get out. The 

 audible effects could be studied by placing the ear in communication 

 with the interior of the vessel by means of a hearing-tube. 



Some preliminary experiments were made in Paris to test this idea, 

 and the results were so promising that they were communicated to the 

 French Academy on October 11, 1880, in a note read for me by M. 

 Antoine Breguet.* Shortly afterward I wrote to Mr. Tainter, sug- 

 gesting that he should carry on the investigation in America, as cir- 

 cumstances prevented me from doing so myself in Europe. As these 

 experiments seem to have formed the common starting-point for a 

 series of independent researches of the most important character, car- 

 ried on simultaneously, in America by Mr. Tainter, and in Europe by 

 M. Mercadier,f Professor Tyndall,J: W. E. Rontgen,* and W. H. 

 Preece,|| I may be permitted to quote from my letter to Mr. Tainter 

 the passage describing the experiments referred to : 



Metropolitan Hotel, Eue Cambon, Paris, November 2, 1880. 



Dear Me. Tainter : . . . I have devised a method of producing sounds by 

 the action of an intermittent beam of light from substances that can not be ob- 

 tained in the shape of thin diaphragms or in the tubular form ; indeed, the meth- 

 od is specially adapted to testing the generality of the phenomenon we have dis- 

 covered, as it can be adapted to solids, liquids, and gases. 



Place the substance to be experimented with in a glass test-tube, connect a 



* " Comptes Rendus," vol. cxl, p. 595. 



f "Notes on Kadiophony " (" Comptes Rendus," December 6 and 13, 1880 ; February 

 21 and 28, 1881). See, also, " Journal de Physique," vol. x, p. 53. 



X "Action of an Intermittent Beam of Radiant Heat upon Gaseous Matter" ("Pro- 

 ceedings of the Royal Society," January 13, 1881, vol. xxxi, p. 307). 



^ " On the Tones which arise from the Intermittent Illumination of a Gas." (See 

 " Annalen der Physik und Chemie," January, 1881, No. 1, p. 155.) 



II "On the Conversion of Radiant Energy into Sonorous Vibration "(" Proceedings 

 of the Royal Society," March 10, 1S81, vol. xxxi, p. 506). 



