This promise of Edison's, made at the time of his so-called failure and pondered during the years of his tremendous activities, was not redeemed until he had retired from the business of invention as a means of gaining riches. "I am not making these experiments for money," Edison has said many times. "This model represents the character of the house which I will construct of concrete. I believe it can be built by machinery in lots of 100 or more at one location for a price which will be so low that it can be purchased or rented by families whose total income is not more than $550 per annum. It is an attempt to solve the housing question by a practical application of science, and the latest advancement in cement and mechanical engineering." [Illustration: HUGE CONCRETE MOULDS AT PANAMA These great locks are made as monoliths or in moulds of one piece, the whole making the greatest masonry work the world has ever seen.] [Illustration: CONCRETE LOCKS ON THE PANAMA CANAL The Gatun middle locks, east chamber, looking south from the east bank.] Edison's plan, as we have seen before, was simply to make a set of moulds in the shape of the house he desired to build, run the concrete into them, let them stand until the material had settled, and then take down the retaining surfaces, exposing to view the finished house. It was contrary to all the previous ideas in building, and was ridiculed by many famous architects. Nevertheless, tremendous obstacles are the stuff upon which Edison's genius feeds, and he only worked the harder to produce a concrete that would be liquid enough to fill all the intricate spaces and turns in the moulds and yet sufficiently thick to prevent the sand or gravel in the concrete from sinking to the bottom. Thus, it first had to run like thin mush and then set in walls and floors harder than any brick or stone. Another of the difficulties to be overcome was to discover a concrete that would give perfectly smooth walls. Although this may sound very simple, it has not yet been completely worked out in this country, owing to the heavy demands on Edison's time. The perfected process, however, will be made known just as soon as the inventor can find time to complete certain small details that he wants to clear up before giving the system to the world. A French syndicate working along Edison's ideas for a poured house has made some progress and it is reported they have constructed two attractive dwellings with considerable success. One of these is at Santpoort, Holland, and the other near Paris. Whether the houses are poured completely in one mould, or whether they are built a story at a time on different days, this newest form of house building is carried on along about the same lines.