Speculative mechanics began to consider whether it might not be employed as a means of land locomotion.

The comprehensive mind of Sir Isaac Newton had long before, in his 'Explanation of the Newtonian Philosophy,' thrown out the idea of employing steam for this purpose; but no practical experiment was made.

Benjamin Franklin, while agent in London for the United Provinces of America, had a correspondence with Matthew Boulton, of Birmingham, and Dr.Darwin, of Lichfield, on the same subject.

Boulton sent a model of a fire-engine to London for Franklin's inspection; but Franklin was too much occupied at the time by grave political questions to pursue the subject further.
Erasmus Darwin's speculative mind was inflamed by the idea of a "fiery chariot," and he urged his friend Boulton to prosecute the contrivance of the necessary steam machinery.[6] Other minds were at work.

Watt, when only twenty-three years old, at the instigation of his friend Robison, made a model locomotive, provided with two cylinders of tin plate; but the project was laid aside, and was never again taken up by the inventor.