EDISON, THOMAS ALVA. AUTOGRAPH LETTER SIGNED TO HENRY PARHAM, REGARDING INFORMATION ON NATURAL GAS

1 page (8 1/2 x 10 5/8 in.; 210 x 270 mm) on Edison Elictric Light Company letterhead, written in black ink. Dated April 10, 1881, signed ("Thomas Edison"); repairs to folds, a few stray spots. [With]: part of envelope addressed in Edison's hands, mounted on paper. 

A letter by one of America's most renowned inventors, extolling the virtues of the electric light  "I am about to give Mr. Kennedy a chance to show how cheap he can make gas by entering into a competition with the Electric Light," Edison writes to Parnham. About a year and a half before drafting this letter, Edison had finally succeed in in perfecting an incandescent lamp.  By early 1881, as this letter attests, Edison was ready to claim that gas illuminations were no longer competitive with the electric light.