Which sentence from "The Early History of the Generation and Use of Steam" is the thesis sentence?

"While the time of man’s first knowledge and use of the expansive force of the vapor of water is unknown, records show that such knowledge existed earlier than 150 B. C."
"To the next contributor, Edward Somerset, second Marquis of Worcester, is apparently due the credit of proposing, if not of making, the first useful steam engine."
"The steam engine first became commercially successful with Thomas Savery."
"In 1711, this engine was introduced into mines for pumping purposes."