es the printing
hammers. The paper is sufficiently long for 1200 observations including
spacing between records. The operation of the printing hammers is such that
the uniform motion of the type wheel is not disturbed in the act of
printing. The whole instrument is mounted on a heavy slate plate 45 cm. by
60 cm., and protected by a glass cover.

The manipulation of the apparatus is extremely simple and convenient and
the records obtained are perfectly reliable and accurate within about 0.01
of a second. The saving of time and labor by the printing chronograph is
very considerable and the filing of the records very convenient.

This printing chronograph has been in use at the Dearborn Observatory for
about twenty years and during the last five years the following
observatories have been equipped with the instrument: Amherst College
Observatory; Case School of Applied Science, Cleveland; Philadelphia
Observatory; Durham Observatory, Durham, England; Observatory of LaPlatta,
Argentine; and Dominion Observatory, Ottawa, Canada.

Prof. Hough has kindly consented to inspect every chronograph before it
leaves our shop. Price, complete on stand, glass cover, etc. #$500.00#

[Illustration: A 801]

[Illustration: A 802]

#A801. Laboratory Clock.# This is an eight-day clock; has a movement of the
best workmanship, is driven by two strong springs, and keeps accurate time.
The dial is 12 inches in diameter and has hour, minute and second hands.
Pendulum beats seconds and makes electric contact by means of an adjustable
mercury cup. It is mounted in a hardwood case with glass door.
Price #$27.00#

#A802. Laboratory Clock.# The same as preceding one, but with better clock
movement, gravity driven. Price #$35.00#

#A803. Regulator Clock.# This clock has a first-class eight day movement
with cut steel pinions. It is fitted with mercury compensation pendulum and
electrical seconds contact. Price #$200.00#

#Note.#--We can furnish free of duty to educational institutions
astronomical precision clocks made by C. Riefler, Germany, and will be
pleased to quote prices to interested parties.

[Illustration: A 1200]

#A1200. Simple Comparator.# (Fig. A1200.) Built up of #Micrometer Slide#
M301 and #Microscope# M101, #with support# M310 #Fitted with Stage#. The
stage is 150 mm. long and provided with cli