The question as to the actual cost to the consumer, everything being included, of the light produced by the various illuminating agents now in use has not yet received a clear and definite answer. Careful attention should therefore be paid to any evidence which is based upon a serious study of the question, so that at least some idea of the truth may be gained. It is for this reason that we reproduce below extracts and tables, taken from a paper presented by C. Holland, engineer at Mons, to the Society of Engineers of the Liege Institute, and published in the Revue Universelle des Mines.

According to this author, "it follows from the examination of these tables that lighting by gas, and even by petroleum, is by no means on the point of being replaced by the electric light." These tables establish the fact that under the most favourable conditions for the production of the electric light, that is to say, where spare motive power can be applied to its production, this system of lighting still costs .0152d. per candle power per hour (Table VII.), while gas, costing 1.43d. per cub. metre, burnt in the recuperative lamps of Siemens, or still better, of Wenham, gives a light which only costs '009604d. and even only '006631d. per candle power per hour. (Table II.)