of rotation each. The
field coils surround the armature, and there is a laminated iron field
structure completing the magnetic circuit. I may say here that
surrounding the armature of a dynamo by the field coils, though very
recently put forth as a new departure, was described in various
Thomson-Houston patents, and to a certain extent all Thomson-Houston
machines embody this feature.

Figs. 15 and 16 will give an idea of the construction of the motor
referred to. CC' are the field coils or inducing coils, which alone are
put into the alternating current circuit. II is a mass of laminated
iron, in the interior of which the armature revolves, with its three
coils, B, B squared, B cubed, wound on a core of sheet iron disks. The commutator
short-circuits the armature coils in succession in the proper positions
to utilize the repulsive effect set up by the currents which are induced
in them by the alternations in the field coils. The motor has no dead
point, and will start from a state of rest and give out considerable
power, but with what economy is not yet known.

A curious property of the machine is that at a certain speed, depending
on the rapidity of the alternations in the coil, C, a continuous current
passes from one commutator brush to the other, and it will energize
electro magnets and perform other actions of direct currents. Here we
have, then, a means of inducing direct currents from alternating
currents. To control the speed and keep it at that required for the
purpose, we have only to properly gear the motor to another of the
ordinary type for alternating currents, namely, an alternating-current
dynamo used as a motor. The charging of storage batteries would not be
difficult with such a machine, even from an alternating-current line,
though the losses might be considerable.

* * * * *

PHOTOGRAPHIC STUDY OF STELLAR SPECTRA, HARVARD COLLEGE OBSERVATORY.

HENRY DRAPER MEMORIAL.

_First Annual Report_.

Dr. Henry Draper, in 1872, was the first to photograph the lines of a
stellar spectrum. His investigation, pursued for many years with great
skill and ingenuity, was most unfortunately interrupted in 1882 by his
death.

The recent advances in dry-plate photography have vastly increased our
powers of dealing with this subject. Early in 1886, accordingly, Mrs.
Draper made a liberal provision for carrying on this investigation at
the Harvard College Observatory, as a m