of phosphorescence which Crookes' elicits by the action of his radiant matter. In like manner the thermic and the mechanical effects are most simply explained, according to the expression selected by Crookes himself, as the results of a "continued molecular bombardment." The attraction of the so called radiant matter, regarded as a stream of metallic particles by the magnet, will not appear surprising. * * * * * ECONOMY OF THE ELECTRIC LIGHT. Mr. W. H. Preece writes to the _Journal of Arts_ as follows: At the South Kensington Museum, very careful observations have been made on the relative cost of the two systems, _i. e._, gas and electricity. The court lighted is that known as the "Lord President's" (or the Loan) Court. It is 138 feet long by 114 feet wide, and has an average height of about 42 feet. It is divided down the middle lengthwise by a central gallery. There are cloisters all around it on the ground floor, and the walls above are decorated in such a way that they do not assist in the reflection or diffusion of the light. The absence of a ceiling--the court being sky-lighted--is to some extent compensated for by drawing the blinds under the sky-lights. The experiments commenced about twelve months ago, with eight lamps only on one side of the court. The system was that of Brush. The dynamo machine was driven by an eight horse-power Otto gas engine, supplied by Messrs. Crossley. The comparison with the gas was so much in favor of electricity, and the success of the experiment so encouraging, that it was determined to light up the whole court. The gas engine, which was not powerful enough, was replaced by a 14-horse power "semi-portable" steam engine, by Ransomes & Co., of Ipswich--an engine of sufficient power to drive double the required number of lights. The dynamo machine is a No. 7 Brush. There are sixteen lamps in all--eight on each side of the court. The machine has given no trouble whatever, and it has, as yet, shown no signs of wear. The lamps were not all good, and it was found that they required careful adjustment, but when once they were got to go right they continued to do so, and have, up to the present, shown no signs of deterioration, although the time during which they have been in operation is nine months. The first outlay has been as follows: Engine and fixing, including shafting and belting................................ £420 Dynamo machine......................... 400 Lamps, apparatus, and conducting wire . 384 ------ £1,204 The cost of working has been, from June 22, to December 31, during which period the lights were going on 87 nights for a total time of 359 hours: