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We present here the Calar Alto Schmidt-Lemaitre Telescope (CASTLE) concept, a technology demonstrator for curved detectors, that will be installed at the Calar Alto Observatory (Spain). This telescope has a wide field of view (2.36x1.56 deg^2) and a design, optimised to generate a Point Spread Function with very low level wings and reduced ghost features, which makes it considerably less susceptible to several systematic effects usually affecting similar systems. These characteristics are particularly suited to study the low surface brightness Universe. CASTLE will be able to reach surface brightness orders of magnitude fainter than the sky background level and observe the extremely extended and faint features around galaxies such as tidal features, stellar halos, intra-cluster light, etc. CASTLE will also be used to search and detect astrophysical transients such as gamma ray bursts (GRB), gravitational wave optical counterparts, neutrino counterparts, etc. This will increase the number of precisely localized GRBs from 20% to 60% (in the case of Fermi/GMB GRBs)., Comment: 29 pages, 11 figures

Three photo-electric effects for certain samples of ${\mathrm{Cu}}_{2}$O and Se as functions of wave-length.---Light from a tungsten lamp or iron arc was dispersed by a quartz spectrometer. Measurements with a thermocouple enabled all results to be reduced to unit light intensity. The observations agree well with previous results obtained with various samples. (1) Decrease of resistance was measured for the range 3900 to 6000 A for ${\mathrm{Cu}}_{2}$O, maximum at 4600 A, and for 4300 to 9300 A for Se, maximum at 7000 A. (2) Photo-electrolytic potential was found to exist for both back (contact with air) and front (contact with distilled water) illumination, and was measured in the case of front illumination for the range 2700 to 5500 A for ${\mathrm{Cu}}_{2}$O (maximum at 3500 A, upper limit about 5600 A), and for 2700 to 9000 A for Se (maximum at 5700 A, upper limit about 9500 A). The effect was positive and proportional to the intensity $I$ for ${\mathrm{Cu}}_{2}$O and to ${I}^{\frac{2}{3}}$ for Se. (3) Photo-electric wave-length limit was found by the use of absorption screens to be at about 2570 A for ${\mathrm{Cu}}_{2}$O and at 2260 A for Se. For both ${\mathrm{Cu}}_{2}$O and Se, all samples showed the same photo-electric limits and those which showed a change of resistance also showed the photo-electrolytic effect, but not vice-versa.

An examination of the Ca $K$ absorption edge in the x-ray absorption spectra of different compounds shows clearly that the secondary structure is not the same in different compounds, and is not even the same in the two crystals calcite and aragonite, which are the same chemically, but of different crystalline form. These facts are in accord with Kronig's theory of the secondary structure. In four other crystals, each of which contains two or more metals, the secondary structure was examined to see if it was the same for the two elements in the same crystal. There is a difference for the two elements, which indicates that the crystal form is not the sole factor in determining the secondary structure.

RECENTLY we have had occasion to make thin films of celluloid by the previously known method of dissolving the celluloid in amyl acetate and allowing a single drop of the solution to fall on a clean water surface. With solutions sufficiently dilute, as the amyl acetate evaporates interference colours appear in practically uniform sheets of colour over the entire surface which change from red to violet and then the film becomes colourless. Some of these films were deposited on optically flat glass and their thickness determined by an interferometer method by C. G. Peters, of the Bureau of Standards' staff.