Would it not be possible for the United States Geological Survey to enforce rules which would prevent the existence of conditions such as those mentioned? The Survey is doing wonderful work, as shown by the rescue of twenty miners at Cherry one week after the conflagration; but there is no doubt that perhaps all the men could have been saved if telephone communications with the outside had been established. Telephone lines to resist any kind of a fire, can easily be installed, and the expense is small, almost negligible when one considers the enormous losses suffered by the mine owners and by the families of the victims. H. G. STOTT, M. Am. Soc. C. E.--The curves shown by Mr. Wilson give a clear general idea of the relative efficiencies of steam and gas engines when treated from a purely theoretical thermodynamic point of view. This point of view, however, is only justified when small units having a maximum brake horse-power not exceeding 1,000 are considered. The steam engine or turbine operating under a gauge pressure of 200 lb. per sq. in., and with 150° superheat, has a maximum temperature of 538° Fahr. in its cylinder, while that of the gas engine varies between 2,000° and 3,000° Fahr. The lubrication of a surface continually subjected to the latter temperature would be impossible, so that water jackets on the cylinders and, in the larger units, in the pistons become absolutely necessary. As the cylinders increase in diameter, it is necessary, of course, to increase their strength in proportion to their area, which, in turn, is proportional to the square of the diameter. The cooling surface, however, is only proportional to the circumference, or a single function of the diameter. Increasing the strength in proportion to the square of the diameter soon leads to difficulties, because of the fact that the flow of heat through a metal is a comparatively slow process; the thick walls of the cylinders on large engines cannot conduct the heat away fast enough, and all sorts of strains are set up in the metal, due to the enormous difference in temperature between the inside and the jacket lining of the cylinder. These conditions produce cut and cracked cylinders, with a natural resultant of high maintenance and depreciation costs. These costs, in some cases, have been so great, not only in the United States, but in Europe and Africa, as to cause the complete abandonment of large gas engine plants after a few years of attempted operation.