IF the canals of Mars are structures made by intelligent beings, it is difficult to believe that these beings have not at their disposal appliances both for construction and survey. It is difficult to believe that some of these appliances are not made of metal. If made of metal, it is difficult to believe that the Martians do not use fire. There is strong evidence that friction was the source of the discovery of fire on the earth. But is it likely that fire would be discovered by friction on a planet the barometrical pressure of which is less than 4 inches of mercury, and the still atmosphere of which is believed to be free from thunderstorms and lightning flashes?