of coal per hour.

While the chemist is busy with his researches for substances and
combinations which will yield great power with small quantities of
material, the engineer assiduously endeavors to reconvert the chemical
or electrical energy into mechanical work suitable to the various needs.

To get the maximum amount of work with a minimum amount of weight, and
least dimensions combined with the necessary strength is the province
of the mechanical engineer--it is a grand and interesting study; it
involves many factors; it is not, as in the steam engine and hydraulic
machine, a matter of pressures, tension and compression, centrifugal and
static forces, but it comprises a still larger number of factors, all
bearing a definite relation to each other.

With dynamo machines the aim has been to obtain as nearly as possible
as much electrical energy out of the machine as has been put in by the
prime mover, irrespective of the quantity of material employed in its
construction. Dr. J. Hopkinson has not only improved upon the Edison
dynamo, and obtained 94 per cent. of the power applied in the form of
electrical energy, but he got 50 horse power out of the same quantity of
iron and copper where Edison could only get 20 horsepower--and, though
the efficiency of this generator is perfect, it could not be called an
efficient motor, suitable for locomotion by land or water, because it
is still too heavy. An efficient motor for locomotion purposes must not
only give out in mechanical work as nearly as possible as much as the
electrical energy put in, but it must be of small weight, because it has
to propel itself along with the vehicle, and every pound weight of
the motor represents so many foot pounds of energy used in its own
propulsion; thus, if a motor weighed 660 pounds, and were traveling at