CHAPTER XXII. 



SUNDRY ELECTRICAL APPLIANCES MR. EDISON'S INVENTIONS THE: 



ELECTRIC LIGHT THE GYROSCOPE A NEW ELECTROPHORUS - 



ELECTRIC TOYS. 



THE ELECTRO-MOTOGRAPH although perhaps even yet scarcely developed 

 has already proved a very useful invention. The idea of it first occurred 

 to Mr. Edison in 1873, when he was prosecuting some researches in 

 chemical telegraphy. " One day," says Mr. Fox, in his account of the 

 invention, " as he sat pondering over his work, he happened to take in 

 hand the metallic point through which, as it rested upon the paper, the 

 current was wont to pass. When again he closed the circuit to let the 

 current through the paper, he held the metallic point loosely, and uninten- 

 tionally allowed it to rest upon the paper. Every time he moved the- 

 metallic strip on the paper the latter became wonderfully smooth. Edison 

 was determined to find the reason of this, and he decided that the electricity 

 very much lessened the friction of the metal on the paper. He made many 

 experiments, and brought the subject before the Royal Society in 1874, but 

 nothing came of the idea till 1876, when Edison was perfecting his musical 

 telephone. 



" The new appliance is, in fact, the same invention revived and now 

 perfected by the original inventor, and brought to complete practical success, 

 under the title of the * electro-motograph.' The action of the ' electro- 

 motograph ' depends on the fact, discovered during former experiments, and 

 employed imperfectly in the musical telephone, that the friction of moving 

 bodies varies in greater or less degree with their electrical condition. In< 

 the electro-motograph a cylinder made of prepared chalk, and saturated 

 with a. strong solution of caustic alkali, is set upon supports, so that it can 

 be turned upon its axis. A strip of metal fastened to the mica diaphragm 

 rests on the cylinder, and is pressed so firmly by its spring upon the 

 cylinder that when it is turned by means of the handle the friction of the 

 strip on the cylinder tends to pull the diaphragm out of shape, causing it 

 to bulge inward as long as the cylinder is in motion. If now, while this, 

 motion of the cylinder is maintained, an electric current passes through the 

 strip of metal, and then through the chalk cylinder to earth, the amount 

 of this friction is varied or it is destroyed altogether, and the strip slides 

 freely on the cylinder. This was the basis of the former invention. The 



