In 1840 Draper published the result of certain important experiments made by him in photographing celestial bodies. In 1841 pneumatic caissons were invented by Triger in France. In 1842 Long discovered the usefulness of ether as an anæsthetic, and Seytre invented the automatically played piano. In the same year, Selligne discovered a method of utilizing water-gas, made by decomposing water and producing a new illuminating agent that could be used by itself or in combination with coal gas. In the same year James Nasmyth in Scotland invented the steam hammer--a simple appliance by means of which steam was able to make a hammer give blows much heavier than the human arm could give. This invention belongs to the class in which the human muscles are assisted in doing work which the brain directs them to do, but which they are not strong enough to do effectively. The self-playing piano belongs in a class closely allied, in which the machine invented merely assists the muscles: the assistance in this class being not in supplying power in order to do more work, however, but in supplying what may be called auxiliary physical agencies. In the player piano, the fingers are replaced by little mechanical hammers; in the steam hammer the arm is replaced by a piston actuated by steam. One secures quickness, the other secures force. But the self-playing piano and the steam hammer are in very different classes, when viewed from the standpoint of their influence on history. The influence of the piano is scarcely discernible, while the influence of the steam hammer stands out in enormous letters of steel. The piano seems to be in the same category as are literature and poetry and music in general: it serves to please. The steam-hammer, on the other hand, has had so great an influence on history subsequent to its invention, that we know that subsequent history could not have been as it has been, if the steam hammer had not been invented.