Several decades elapsed after Faraday's initial experiment before the phenomena of magneto-electricity were proved to have any considerable commercial significance. A vast amount of ingenuity was required to devise a mechanism which could advantageously utilize the principle in question for commercial purposes. Indeed the early experimenters did not at once get upon the right track, as their efforts were influenced disadvantageously by an attempt to follow the principle of the steam engine. Some interesting mechanisms were devised whereby the motion of an armature in being drawn toward an electromagnet could be translated into rotary motion through the use of crank-shafts and even of beams, precisely comparable to those employed in the steam engine. Such devices worked with a comparatively low degree of efficiency and were totally abandoned so soon as the idea of getting rotary motion directly from the magnet or armature was made feasible. The names of Saxton, Clarke, Woolrich, Wheatstone, and Werner Siemens are intimately connected with the early efforts at utilization of magneto-electric power. The shuttle-wound armature of Siemens, invented in 1854, marked an important progressive step. PERFECTING THE DYNAMO The first separately excited dynamos were constructed by Dr. Henry Wilde, F.R.S., between 1863 and 1865, and this invention paved the way for rapid progress. In 1866-7 Varley, Siemens, Wheatstone, and Ladd constructed machines with several iron electromagnets, self-excited, which were described as dynamo-electric machines, a term afterward contracted to dynamos. In 1867 Dr. Wilde improved the armature by introducing several coils arranged around a cylinder; the current from a few of the coils was rectified and used to excite the field magnet, while the main current as given off by the rest of the coils was taken off by ring-contacts, the machine being a self-exciting, alternating-current dynamo. [Illustration: WILDE'S SEPARATELY EXCITED DYNAMO. Dr. Wilde invented and patented (1863-5) the first separately excited dynamo, with which he demonstrated that the feeble current from a small magneto-electric machine would, by the expenditure of mechanical power, produce currents of great strength from a large dynamo.] The Italian, Picnotti, in 1864 invented a ring armature which, although provided with teeth was wound with coils in such a way as to obtain a very uniform current; but the practical introduction of the continuous-current machines dates from 1870, when Gramme re-invented the ring and gave it the form which is still in vogue. Von Alteneck in 1873 converted the Siemens shuttle armature along the same lines and so introduced the drum arrangement which has since been very extensively adopted.