The lighting of a sky-scraper is a most elaborate arrangement. Some of them use as many lights as would well supply a good sized town. The Singer Building in New York has 15,000 incandescent lamps and it is safe to say the Metropolitan Life Insurance Building has more than twice this number as the floor area of the latter is 2-1/2 times as great. The engines and dynamos are in the basement and so fixed that their vibrations do not affect the building. As space is always limited in the basements of sky-scrapers direct connected engines and dynamos are generally installed instead of belt connected and the boilers operated under a high steam pressure. Besides delivering steam to the engines the boilers also supply it to a variety of auxiliary pumps, as boiler-feed, fire-pump, blow-off, tank-pump and pump for forcing water through the building. The heating arrangement of such a vast area as is covered by the floor space of a sky-scraper has been a very difficult problem but it has been solved so that the occupant of the twentieth story can receive an equal degree of heat with the one on the ground floor. Both hot water and steam are utilized. Hot water heating, however, is preferable to steam, as it gives a much steadier heat. The radiators arc proportioned to give an average temperature of 65 degrees F. in each room during the winter months. There are automatic regulating devices attached to the radiators, so if the temperature rises above or falls below a certain point the steam or hot water is automatically turned on or off. Some buildings are heated by the exhaust steam from the engines but most have boilers solely for the purpose. The sanitary system is another important feature. The supplying of water for wash-stands, the dispositions of wastes and the flushing of lavatories tax all the skill of the mechanical engineer. Several of these mighty buildings call for upwards of a thousand lavatories. In considering the sky-scraper we should not forget the role played by the electric elevator. Without it these buildings would be practically useless, as far as the upper stories are concerned. The labor of stair climbing would leave them untenanted. No one would be willing to climb ten, twenty or thirty flights and tackle a day's work after the exertion of doing so. To climb to the fiftieth story in such a manner would be well-nigh impossible or only possible by relays, and after one would arrive at the top he would be so physically exhausted that both mental and manual endeavor would be out of the question. Therefore the elevator is as necessary to the skyscraper as are doors and windows. Indeed were it not for the introduction of the elevator the business sections of our large cities would still consist of the five and six story structures of our father's time instead of the towering edifices which now lift their heads among the clouds.