272 



ELECTRIC LIGHT. 



therefore of the light, rises in proportion as the 

 carbons are consumed. In the ingenious lamps 

 of M. Lontin the resistance is also constant, ir- 

 respective of the length of the carbon rods. 



In another of M. Rapieff 's lamps the two 

 pairs of carbon rods are placed not one above 

 the other, but side by side. The arc is pro- 

 duced at the junction of the four points, and 

 the effect is considerably increased by the pres- 

 ence of a cylinder of lime, which is placed 

 above the light, and contributes by its incan- 

 descence to increase the intensity of the light. 



In the various forms of electric lamp thus far 

 described, and in many others which there is 

 not space here to mention, the carbon pencils 

 are separated to a certain distance, and across 

 this the voltaic arc is produced. A form of 

 lamp has, however, been lately invented by 

 Mr. Richard Werdermann in which the light is 

 produced while the carbons are in direct con- 

 tact. The lamp (Fig. 4) is therefore reduced 

 to extreme simplicity of construction. 



FIG. 4. 



In the ordinary arrangement in which the 

 two pencils are of equal sectional area, the end 

 of the positive carbon is worn into a crater- 

 like shape, and from this pole the greater part 

 of the light is emitted ; on the other hand, the 

 negative carbon is formed into a cone, and 

 becomes but slightly luminous. Werdermann 

 found that, by increasing the sectional area of 

 the negative electrode, its consumption is di- 

 minished, and if it be sufficiently large it suffers 

 no appreciable loss during the passage of the 

 current. He therefore uses in his lamp two 

 carbons which are extremely unlike each oth- 

 er both in size and shape. The negative car- 

 jon 0, supported by the bracket B, is a disk 

 flat on one side and curved on the other, its 

 shape being not unlike that of a bun. The di- 

 ameter of this disk is about two inches and its 

 thickness one inch. The curved surface of the 

 : is directed downward, and against this 

 surface the positive carbon c is pressed. This 

 rbon is in the form of a thin pointed pencil 



three millimetres in diameter. It is held by 

 means of a spring collar in a metallic tube in 

 which it slides vertically up and down. A 

 cord connects the clasp D at the bottom of the 

 rod, and the balance W, by which the rod is 

 held in contact with the disk. On the passage 

 of the current a very small electric arc is pro- 

 duced, but it is remarkable for steadiness and 

 for purity of color. Round the upper part of 

 the disk is a metallic band A, to which the 

 circuit wire is attached, and the current is thus 

 passed on to the next lamp. With this lamp 

 the electric light may be obtained from an 

 electro-motor of very low power. With a 

 small Gramme machine driven by a two-horse- 

 power engine, and yielding an electro-motive 

 force equivalent to only about four Daniell's 

 cells, ten of these electric lamps were placed 

 in circuit at once. The light, even with large 

 lamps of three hundred candle-power, is of so 

 soft a character that it appears unnecessary to 

 protect it with globes of opal glass. 



A lamp, not altogether unlike Werdermann's 

 in principle, has been constructed by M. Rey- 

 nier. In this arrangement a carbon pencil 

 presses directly against the edge of a circu- 

 lar disk of carbon which revolves in a ver- 

 tical plane. The pencil forms the positive elec- 

 trode, and the current enters not far from the 

 pointed extremity in contact with the disk. 

 As the carbon burns away it is urged forward 

 by a simple mechanism, and thus contact is 

 never broken. The residuum, or ash, left by 

 the combustion of the positive carbon is con- 

 tinuously removed by the rotation of the neg- 

 ative disk. It is stated that this lamp gives a 

 clear light with only a small electro-motive 

 force, and that several lamps may be operated 

 by the same current. 



A novel form of electric lamp has been pat- 

 ented by Mr. W. Wallace, of Ansonia, Connecti- 

 cut, which realizes still greater simplicity in its 

 construction. Its peculiarity (Fig. 5) lies main- 



FIG. 5. 



ly in the shape of the carbons, which, instead of 

 being either pencils or circular disks as in oth- 

 er lamps, take the form of rectangular slabs A 

 and B, each about nine inches in length and 

 three inches in breadth. The thickness varies 

 in the two electrodes, the positive carbon B 



