PREFACE TO THE SECOND EDITION.

I have endeavoured in the present Edition to lay before my readers the various improve-ments that have been made in the Manufacture of Gas since 1841, and I have to acknow-ledge the' valuable assistance I have received from my friend Dr. Frankland, who has revisedthe Chapter on the Chemistry of Coal-Gas. To Dr. Lyon Playfair I am indebted for muchimportant information ; and Mr. William Pole has enabled me to perfect the subject of theDistribution of Gas through Mains, the Chapter upon the theory of the motion of elasticfluids through pipes being entirely from his pen. It will be perceived that I have retainedin this Edition descriptions of many portions of apparatus that have ceased to be employed :and I have done so simply that their history may be preserved, since it is often as useful toknow what machinery is defective, as to be acquainted with that which is more perfect. Theanalysis of the various kinds of coal found in different parts of the world cannot, I think,fail to be of value. I have been careful, throughout the Work, to enlarge only upon thosepoints on which experience has enabled me to speak with certainty.

S. C.

London, April 6 th, 1S53.