for it.

This is all very well. It is certain that most of the smoke made in
manufacturing concerns can be consumed, if manufacturers are compelled
by law to erect sufficient heating surface and to include the well-known
appliances, including those for careful firing, but no city so far as
the writer knows has ever been able to enforce effective laws. There
remain the dwellings of the people to deal with, which give forth smoke
in large cities in the aggregate far exceeding that made by the
manufacturing plants. New York pursues the only plan for ensuring the
clearest skies of any large city in the world where coal is generally
used, by making the use of bituminous coal unlawful. The enormous growth
of present New York (45 per cent. in last decade) is not a little
dependent upon the attraction of clear blue sides and the resulting
cleanliness of all things in and about the city compared with others.
When, by the progress of invention or new methods of distributing heat,
smoke is banished, as it probably will be some day, many rich citizens
will remain in their respective western cities instead of flocking to
the clear blue-skied metropolis, as they are now so generally doing.

Such were some of Watt's by-products. His recreation, if found at all,
was found in change of occupation. We read of no idle days, no pleasure
trips, no vacations, only change of work.

Rumors of new inventions of engines far excelling his continued to
disturb Watt, and much of his time was given to investigation. He
thought of a caloric air engine as possibly one of the new ideas; then
of the practicability of producing mechanical power by the absorption
and condensation of gas on the one hand and by its disengagement and
expansion on the other. His mind seemed to range over the entire field
of possibilities.

The Hornblower engine had been heralded as sure to displace the Watt.
When it was described, it proved to be as Watt said, "no less than our
double-cylinder engine, worked upon our principle of expansion. It is
fourteen years since I mentioned it to Mr. Smeaton." Watt had explained
to Dr. Small his method of working steam expansively as early as May,
1769, and had adopted it in the Soho engine and also in the Shadwell
engine erected in that year.

We have seen before that Watt had to retrace his steps and abandon for a
time in later engines what he had before ventured upon.

The application of steam for propelling boats upon the water