It was during this period of "inventing a system" that so much systematic and continuous work with good results was done by Edison in the design and perfection of dynamos. The value of his contributions to the art of lighting comprised in this work has never been fully understood or appreciated, having been so greatly overshadowed by his invention of the incandescent lamp, and of a complete system of distribution. It is a fact, however, that the principal improvements he made in dynamo-electric generators were of a radical nature and remain in the art. Thirty years bring about great changes, especially in a field so notably progressive as that of the generation of electricity; but different as are the dynamos of to-day from those of the earlier period, they embody essential principles and elements that Edison then marked out and elaborated as the conditions of success. There was indeed prompt appreciation in some well-informed quarters of what Edison was doing, evidenced by the sensation caused in the summer of 1881, when he designed, built, and shipped to Paris for the first Electrical Exposition ever held, the largest dynamo that had been built up to that time. It was capable of lighting twelve hundred incandescent lamps, and weighed with its engine twenty-seven tons, the armature alone weighing six tons. It was then, and for a long time after, the eighth wonder of the scientific world, and its arrival and installation in Paris were eagerly watched by the most famous physicists and electricians of Europe.