of supply. The genesis of his invention Mr. Callahan has told in an
interesting way: "In 1867, on the site of the present Mills Building on
Broad Street, opposite the Stock Exchange of today, was an old building
which had been cut up to subserve the necessities of its occupants, all
engaged in dealing in gold and stocks. It had one main entrance from the
street to a hallway, from which entrance to the offices of two prominent
broker firms was obtained. Each firm had its own army of boys, numbering
from twelve to fifteen, whose duties were to ascertain the latest
quotations from the different exchanges. Each boy devoted his attention
to some particularly active stock. Pushing each other to get into these
narrow quarters, yelling out the prices at the door, and pushing back
for later ones, the hustle made this doorway to me a most undesirable
refuge from an April shower. I was simply whirled into the street.
I naturally thought that much of this noise and confusion might be
dispensed with, and that the prices might be furnished through some
system of telegraphy which would not require the employment of skilled
operators. The conception of the stock ticker dates from this incident."

Mr. Callahan's first idea was to distribute gold quotations, and to
this end he devised an "indicator." It consisted of two dials mounted
separately, each revolved by an electromagnet, so that the desired
figures were brought to an aperture in the case enclosing the apparatus,
as in the Laws system. Each shaft with its dial was provided with two
ratchet wheels, one the reverse of the other. One was used in connection
with the propelling lever, which was provided with a pawl to fit into
the teeth of the reversed ratchet wheel on its forward movement. It was
thus made impossible for either dial to go by momentum beyond its limit.
Learning that Doctor Laws, with the skilful aid of F. L. Pope, was
already active in the same direction, Mr. Callahan, with ready wit,
transformed his indicator into a "ticker" that would make a printed