U KANSAS CITY REVIEW OF SCIENCE. 



hurricanes has revealed itself to Prof. Bell and M. Janssen in the photophone as 

 feeble echoes, like the murmuring noise due to the flickering of the electric light. 

 It often happens that in pursuing one line of research a man of science is led 

 into another; and Prof. Bell, in seeking to improve his photophone, arrived at 

 what appears to be a new discovery of moment. It has long been known that 

 when a bar of iron is rapidly magnetized and demagnetized, it gives out a musi- 

 cal note of a pitch corresponding to the number of magnetic impulses per minute ; 

 and Prof. Bell found that all kinds of diverse bodies were rendered tuneful by the 

 impact of an intermittent beam of light. Thin disks of wood, glass, metal, ivory, 

 india-rubber and so on, yielded a very distinct note. The apparatus he devised 

 for these experiments is a mirror reflecting a powerful beam of light from the sun 

 or an electric lamp, through a lens, and in the path of the beam is mounted a ro- 

 tating wheel, perforated round the rim with a circle of holes This wheel acts as 

 a screen to the light, except when one of the hole? comes opposite the track of 

 the beam. The latter then passes on to a pair of lenses, which direct the paral- 

 lel beam toward the surface of a thin disk of the material under examination. 

 When the wheel is rotated, the intermitted beam of light falling upon the disk 

 behind causes it to ring with a musical tone whose pitch depends on the number 

 of flashes per minute, and the ear-tube attached enables the listener to hear it 

 without interference. This musical photophone is in reality a light-syren, like the 

 air-syren of Cagniard de la Tour, in which the puffs of air escaping through the 

 holes of a revolving disk emit a note. The disk form, though advantageous, is 

 not essential to the eff'ect. Crystals of sulphate of copper, chips of pine, even 

 tobacco smoke held in a glass test-tube before the beam, are found to yield a 

 beautiful tone. Nor is it necessary that there should be light, for if the light- 

 rays be cut off by a thin sheet of hard rubber or vulcanite, the invisible heat-rays 

 which pass through the opaque screen are capable of producing the effect. In- 

 deed, it is still a moot point among investigators whether the effect may not be due 

 entirely to the vibratory expansion and contraction of bulk due to the recurring 

 blows of the heat-rays. So distinct is the eff'ect that the naked ear held to the 

 disc appreciates it, and even the outer ear itself acts as a receiver, for when the 

 intermittent beam is simply focused in the aural cavity a faint musical note is 

 heard. 



Beside their practical promise, these interesting achievements of Prof. Bell 

 have a poetic bearing. We are at once reminded of that mystical stone of Mem- 

 non which the sunshine made harmonious, and can imagine how the chequered 

 sunshine of trembling leaves is musical to finer ears than ours. In Dean Mil- 

 man's " Martyr of Antioch " the god Phoebus-Apollo is invoked by the chorus of 

 maidens as — 



" Lord of the speaking lyre 



That with a touch of fire 



Strik'st music which delays the charmed spheres." 

 And truly the deep connection between light and music is curiously exemplified in 

 the photophone. Prof. Bell, indeed, has played the part of a god, for has he not 



