When we hitherto on the authority of Lowell, Very, and others, have assumed an average temperature of +10° C. (50° F.) on Mars, we have done so on the supposition that the atmosphere of the planet contained great quantities of heat-conserving gases. This assumption appears to be no more tenable than the belief in the high temperature on Mars. After all, the temperature is probably about 10° C. (18° F.) higher than our last calculation would indicate--or about -40° C. (-40° F.)--because the air on Mars is very clear and admits, therefore, all sun-rays, retaining also a fraction by virtue of what little water vapour, carbon dioxide, and other heat-conserving gases there may be present in the atmosphere. The mean summer temperature at the martian equator (-27° C. or -16.6° F. acc. to Campbell’s data) would then lie about 13° C. (23.4° F.) above the mean for the planet. This agrees closely with conditions on the Earth where the highest mean in July at the equator is 27° C. (80.6° F.) and the mean for the earth 16° C. (60.8° F.). We are consequently obliged to revise in their entirety our ideas about Mars. The belief that organic life (green vegetation) causes the colour of the so-called seas on Mars, as assumed by Lowell, or that the red tints belong to the gorgeous dress in which autumn arrays the plants before their leaves are shed under the attacks of frost, as intimated by Flammarion, must nowadays take its place in the shadowy realm of dreams. Those who do not believe that the so-called canals are real waterways, devoted to freight carrying and irrigation, or illusions, which conception the photographs contradict (for example Fig. 18), generally consider that they signify cracks or fissures. As in the crust of the Earth, they generally run in nearly straight lines or in regularly bent curves (Fig. 17 and 17a). Flammarion mentions that the renowned physicist Fizeau looked upon the “canals” as cracks in the ice-coverings of the oceans on Mars. Penard, in 1888, expressed the more likely opinion that they correspond to the fissures in the crust of the Earth. Flammarion contends that such fissures do not have the rectilinear configuration of the “canals.” This is completely in error, as shown on the map here reproduced (Fig. 16). It is also stated that they are so inexplicably long, for instance the canal Phison is 2250 English miles (Lowell) or 3620 km. in length. The longest known earthquake crack along the entire length of which a dislocation has taken place _at one time_ is 600 km. (373 miles) in extension; the violent earthquake in California, 1906, originated from this crack. There is no doubt, moreover, that a great fissure in the Earth follows the coast of Chile from Arica to the Strait of Magellan in a nearly north and south direction for a distance of about 32 parallels or 3560 km. (2210 miles). This fissure is almost as long as Phison on Mars. Such cracks exist along the entire coast of the Pacific Ocean. As yet,