The most peculiar formations on the Moon are the so-called “bright streaks” which as a rule issue in almost straight lines from some of the larger craters, particularly Tycho and Copernicus. Those around Tycho (see Fig. 28) do not seem to be either raised above nor depressed below the surroundings to any degree worth mentioning. For this reason they are not visible under oblique illumination as in Fig. 25. They proceed in straight lines independent of elevations. This quality is in striking conformity with the characteristics of fissures on earth as for instance those that traverse the Tyrrhenian Sea and the Calabrian mountains. They also resemble the canals on Mars in this respect. Nasmyth and Carpenter caused a glass ball, containing water under pressure, to break at one point and obtained a system of beams radiating from this point and vividly reminding of the streaks around the lunar craters. The same effect appears if a homogeneous plate, of glass for instance, is broken by a blow in one point. No doubt these streak centres were once centres of collapse although they sometimes now are found at a considerable elevation, like Tycho. This may be the result of a later secular lifting of the rocky substrata like the slow rise of the Scandinavian peninsula. The streaks around Copernicus (see Fig. 29) are very different from those around Tycho. They are not rectilinear and consist next to the crater of distinct mountain chains plainly visible under oblique illumination. They penetrate into Mare Imbrium (Fig. 29 below) crossing the mighty “Carpathian” mountains. Frequently, they are provided with minor volcanoes, as in the streak directed almost straight downward on the figure, _i. e._, to the north. They are obviously volcanic fissures like those on the Earth. [Illustration: Fig. 28. Tycho in full illumination with surrounding magnificent system of streaks. In the lower right corner Copernicus with a less regular system appears. Between them Mare Nubium, in the upper right Mare Humonum, with the great crater Gassendi below. The moon diameter corresponds to 16.7 cm. Photo by Yerkes Observatory. Compare Figs. 25 and 28, showing parts of the same territory under side light. ]