136 ANNUAL OF SCIENTIFIC DISCOVERY. 



case of fixed lights in meridian planes only, while in revolving 

 lights the rays are gathered into a number of cj^lindrical beams, 

 which are made to pass successively before the observer by the 

 rotation of the apparatus. The instrument consists of 3 main 

 divisions ; an equatorial belt of the sphere of light proceeding 

 from the flame is acted upon by refraction, but the rays above and 

 below this belt are deflected by local reflection. The relative illu- 

 minating values in the horizontal plane of these divisions of the 

 part of the luminous sphere acted upon are in the proportion of, 

 upper reflectors, 20 ; refracting portion, 70 ; lower reflectors, 10. 

 It is important to send toward the sea horizon the brightest sec- 

 tions of the flame. 



The machine for the production of the electric light consists 

 essentially of 6 brass wheels, with 16 bobbins of insulated copper 

 attached at equal distances to the circumferences of each wheel ; 

 inside each bobbin is a hollow core of soft iron ; the wheels are 

 all fixed upon a shaft, which is driven by a steam engine. In 

 turning, every core of each wheel is brought at the same instant 

 between the opposite poles of two magnets, which pair of poles 

 it also quits at the same instant. The core of every bobbin has its 

 magnetism thus reversed by the revolution of the wheels 107 

 times per second. This reversing of the magnetism induces a 

 current of electricity in the bobbins ; the combination of the cur- 

 rents produces one of sufficient intensity to give a powerful light. 

 The bars of the lantern are best fixed obliquely, as by this means 

 the least amount of light is stopped by it. 



USE OF ZIRCON IN THE OXYHYDROGEN LIGHT. 



M. Caron has published a memoir on a new material to be sub- 

 stituted for the magnesia cylinders, serving for the ox3iiydrogen 

 light. He found that these cannot resist, indefinitely, the intense 

 heat produced by the combustion of ordinary coal gas mixed with 

 oxygen. This volatilization of the magnesia may be due to the 

 formation of reduced magnesium. After trying silica, alumina, 

 and various refractory substances, he resolved to try zircon, which, 

 according to Berzelius, has the property of being infusible and 

 giving out a light of dazzling brilliancy in the flame of a blow- 

 pipe. This he found to be true, and he has employed the same 

 crayon in the flame of the oxyhdrogen jet, without the least sign 

 of wear, volatilization, or even partial reduction. This is very 

 important, for the incandescent matter must remain always at the 

 same distance, and, if the pencil wore away, the distance would 

 increase and the light diminish. In addition to its being unalter- 

 able, the light is superior to that of magnesia in the proportion of 

 6 to 5. Though at present rare, zircon exists in many volcanic 

 sands, and in great abundance in the zirconean rocks in the en- 

 virons of Ilmensea, at the foot of the Ural Mountains. He has 

 found a simple way of economizing this substance, by applying 

 it only to that portion of the crayon exposed to the flame ; the 

 rest can be made of magnesia or refractory clay. By compres- 



