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63 mcintosh battery and optical co., Chicago, ill., u. s. a. LIGHT FOR PROJECTION. S UNLIGHT excels all other forms of light for projection, but as this work, in many departments, is more conveniently carried on at night, it becomes necessary to seek a substitute. The electric light ranks next to sunlight in brilliancy. An 150 c. p. lamp is made expressly for projection, which produces beautiful results. It can, however, only be employed where it can be connected with a dynamo, which limits its use to such buildings as are supplied with an electric light plant. The light produced from chemical bat- teries is altogether too expensive and troublesome to be employed except in the laboratory for experimental work. Until the problem of producing a compact, portable and economical battery for the pro- duction of the electric light is solved, the majority of projectionists will select the lime-light as practically the best illuminator in the absence of sunlight. A very intense light is produced by forcing a blowpipe flame of mixed hydrogen and oxygen gases upon a stick of unslacked lime. There are four varieties of this light, known as the oxy-hydrogen or Drummond light, the hydro-oxy-calcium light, the oxy-calcium or Bude light, and the ether-oxygen light. In the oxy- hydrogen, two gases are supplied to the jet from separate gasholders, and mix before issuing from the jet. This form of lime-light requires much more expensive and cumbersome apparatus than the others, but has been most used because the most powerful. In the hydro-oxy- calcium, coal gas is used direct from the house fixtures, and does not mix with the oxygen until it issues from the jet. This is the most simple form, but is only about half as powerful as the oxy-hydrogen, and its use is restricted to buildings supplied with coal gas. In the oxy-calcium, an alcohol flame supplies the hydrogen element; it is only about a quarter as powerful as the oxy-hydrogen, but is used in out-of-the-way places to save the trouble and expense of cumbersome hydrogen generators and gasholders. In the ether-oxygen light, ether vapor is substituted for hydrogen or coal gas in the oxy-hydrogen blowpipe, in such a simple and satisfactory manner that it possesses important advantages over every other means for producing the lime- light. This is accomplished by passing a small portion of the oxygen through a saturating chamber of peculiar construction, in which it takes up ether vapor, which it conducts to the jet by way of the