18 SCIENCE IN SHORT CHAPTERS. 



light is visible or rather, renders objects visible I will illus- 

 trate my meaning by means of light. 



Let us suppose three apartments of equal size and same 

 shape, one having its walls covered with mirrors, the second 

 with white paper, and the third with black woollen cloth, and all 

 lighted with central chandeliers of equal brilliancy. The first 

 and second will be much lighter than the third, but they will 

 be illuminated very differently. 



In the first, there will be a repetition of chandeliers in the 

 mirrored walls, each wall definitely reflecting the image of each 

 particular light. In the second room there will be reflection 

 also, and economy of light, but no reflection of definite images ; 

 the apartment will appear to be filled with a general and well- 

 diffused luminosity, rendering every object distinctly visible, 

 and there will be no deep shadows anywhere. 



In scientific language, we shall have, in the first room, regu- 

 lar reflection ; in the second, scattering reflection ; in the third 

 room- we should have comparative gloom, owing to the absorp- 

 tion of the light by the black cloth. 



We may easily suppose the parallels of these in the case of 

 sound. If the velarium and side walls of the transept and 

 orchestra were made of sheet iron, or smooth, bare, unbroken 

 vibrating wooden boards, we should have a certain amount of 

 regular reflection of sound or echo. Just as we should see the 

 particular lights of the chandelier reflected in the first room, so 

 should we hear the particular notes of the singer or player 

 echoed by such regularly vibrating walls and ceiling. 



If, again, the velarium and side drapery of the transept and 

 orchestra had been thick, soft woollen cloths, the sound, like the 

 light, would have been absorbed or " muffled," and, though 

 very clear, it would be weak and insufficient. 



The reader will now ask, What, then, is the right material 

 for such velarium and walls ? I cannot pretend to say what is 

 the best possible, believing that it has yet to be discovered. 

 The best yet known, and attainable at moderate expense, is 

 common canvas or calico, washed or painted over with a mixt- 

 ure of size and lime, or other attainable material that will fill 

 up the pores of the fabric, and give it a moderately smooth 

 face or surface. Thus prepared, it is found to reflect sound, 

 as paper, ground glass, etc., reflect light by scattering rever- 

 beration, but without definite echo. 



It will now be understood how the velarium acted in render- 

 ing the solos so clearly audible at the great height and distance 



