flue situated just above the fire box and carried from the back of the boiler to near the front and then returned to the chimney at the back. [Illustration: Wooden Boilers used in the Philadelphia Water Supply] These wooden boilers were used at the Centre Street waterworks from 1801 to 1815, but did not give general satisfaction on account of the numerous leaks. They were operated at very low pressure, averaging not over 2½ pounds per square inch, but even at this extremely low pressure were found unsatisfactory. During the early days of water supply, following the period of aqueducts, lead was the material commonly used for water supply mains. Later, however, pipes made of bored-out logs were used and continued in service up to the year 1819. The water mains used in Philadelphia were made of spruce logs, reinforced at the ends with wrought-iron bands. A section of one of these old Philadelphia water mains, which is still in a good state of preservation, is on exhibition in the Builders' Exchange of that city. So far as is known, Philadelphia was the first city in the world to adopt cast iron pipe for water mains. Cast iron water pipes were laid in Philadelphia in the year 1804, antedating their use in London, England, by a few years. [Illustration: Section of Bored-out Log Laid in Victoria, B. C., in 1862 and taken out 1900] The durability of wood pipe is rather astonishing when the short life of logs exposed on the surface of the earth is considered. After lying buried in the earth for fifty or sixty years the wood pipe used in the Philadelphia waterworks was sold to Burlington, N. J., in 1804, and remained in constant use there until 1887, when larger mains were required. [Illustration: Valve for Wooden Pipes Used in the Philadelphia Water Supply] [Illustration: Hydrant for Wooden Pipes Used in the Philadelphia Water Supply] Portsmouth, N. H., used bored pine logs for mains from 1798 to 1896, when they were replaced with larger pipes. When dug up, the logs were entirely sound and good for many years' service. A few data regarding the use of wooden pipes might not be without interest, while at the same time pointing out the approximate dates when waterworks were constructed in several cities. Log pipes laid in Victoria, B. C., in 1862 and taken out in 1900 were quite free from decay but badly checked. Constantinople still receives part of its supply through wood pipe. London had 400 miles of wood pipe in use for 218 years, from 1589 to 1807. When taken up it was found to be quite sound. Boston used one system of wood pipes from 1652 to 1796, then replaced it with another one which lasted until 1848. Denver, Colorado, has nearly 100 miles of stave pipe conduit and mains in use. All the water brought to Denver for domestic use passes through wooden pipe 37 inches in diameter, which conducts it from Cherry Creek, which is about 8 miles from center of city.