A French engineer named Duponchel has made a report on the project of a railroad across the Desert of Sahara. The projected railway would run from Algiers to Timbuctoo, a distance of 2,500 kilometers. M. Duponchel stated that the principal portion of the line would rest during nearly its whole extent on layers of sand, and toward the end on primitive volcanic rocks, granite, gneiss, etc. No mountainous obstructions would have to be encountered. The average heat does not appear to exceed 23 deg. or 24 deg. C. (73 2-5 deg. or 75 1-5 deg. Fah.), but account must be taken of the great variations which occur in the 24 hours. For instance, occasionally, a very cold night succeeds a temperature of 40 deg. C. (104 deg. Fah.) in the day time. The great difficulty to be overcome would be the want of water, which is not to be procured in that region. M. Duponchel calculates that for three trains daily the amount of water required would be 4,000 cubic meters, and that the engineering science of the day is quite sufficient to supply even a much greater quantity at the requisite points. The government of Costa Rica has advertised for tenders for building bridges on the second Atlantic Division of its railroad. There will be needed 194 bridges. The bridges will vary in length from 3 feet to 1,044 feet, and will be built for a track of 3 foot 31/2 inch gauge. They will be of sufficient strength to stand a strain of 2,240 lbs. to the lineal foot, in addition to the weight of the usual freight carried. * * * * * THE WERDERMANN ELECTRIC LIGHT. [Illustration: FIG. 1 THE WERDERMANN LAMP.] It has been looked upon as essential that a certain distance should separate the ends of the carbon electrodes used in electric lamps. Every one has accepted this as an axiom. Mr. Werdermann's skepticism has, however, caused him to doubt the axiom, and the result is that he has discarded the electric arc space, and by placing his electrodes in actual contact, has produced a lamp which provides the means of dividing the electric current, and promises to give almost any number of lights from a single machine. Mr. Werdermann's inventions, says the _Engineering_, are secured by patents considerably in advance of those of Mr. Edison, and may in their chief points be explained as follows: