At present we shall say a few words _à propos_ of the engraving we present herewith. The French Crystal Palace will consist of one great nave, two lateral naves, two surrounding galleries, and a vast rotunda behind. The principal entrance, located at the head of the avenue leading from the present ruins (which will, ere long, be transformed into a most interesting museum), will exhibit a very striking aspect with its monumental fountain and the dome which it is proposed to erect over the very entrance itself. The whole structure will cover about nineteen acres of ground, thus being two and a half times the extent of the Palace of Industry in the Champs Elysees. The great nave of honor will be nearly 1,650 ft. in length, 78 ft. in width, and 98 ft. in height. The dome will measure exactly 328 ft. in height, or 105 ft. more than the towers of Notre Dame. The structure, with the exception of basement and foundation, will be of glass and iron. The project which we publish to-day has been studied and gotten up, according to the general plans and dimensions suggested by the promoter, by Mr. Dumoulin, the architect. We are informed that the builder is to be Mr. Alfred Hunnebelle, a contractor well known from the extensive works that he has executed, and who is president of the Syndical Chamber of Contractors of Paris. Among the annexes of this palace we may note a "Palace of the Republic," to be built on the ruins and designed for illustrious or distinguished visitors, such as the President of the Republic, the Ministers, the Municipal Council of Paris, foreign delegates, etc.; a farm house for special exhibitions and a field for experiments; galleries, cottages, etc. As for the programme, which embraces six divisions and numerous subdivisions, we are unable to give it at present for want of space; we need only say that it satisfies perfectly all the conditions of so vast an undertaking. In the hands of the projector, Mr. Nicole, who is well known from his long experience in such matters, the exhibition will undoubtedly prove a success and be instrumental in adding prosperity to all French industries. * * * * * THE GREAT HEAT OF THE SUN.--Prof. S. P. Langley has made the following calculation: A sunbeam one centimeter in section is found in the clear sky of the Alleghany Mountains to bring to the earth in one minute enough heat to warm one gramme of water by 1° C. It would, therefore, if concentrated upon a film of water 1/500th of a millimeter thick, 1 millimeter wide, and 10 millimeters long, raise it 83 1/3° in one second, provided all the heat could be maintained. And since the specific heat of platinum is only 0.0032 a strip of platinum of the same dimensions would, on a similar supposition, be warmed _in one second_ to 2,603° C.--a temperature sufficient to melt it! * * * * * CHATEAU IN THE AEGEAN SEA.