#Note.#--Every instrument is carefully tested before being sent out and we can guarantee the speed not to vary over 1-20 second during the full run of one hour. Large temperature changes will not affect the speed of the clock. A large number of the chronographs are in use and have given excellent satisfaction. [Illustration: A 702] #A702. Prof. G. W. Hough's Printing Chronograph.# The instrument consists of two carefully and accurately constructed clock movements, which are driven by gravity and controlled electrically by the sidereal clock. The movements revolve three type wheels. One of these turns once per second, its edge is divided in 50 parts and it is driven by a separate movement. The second wheel turns once per minute and the third once per hour and they will print the seconds and minutes, while the first will give the hundredths of seconds. A strip of paper is carried over these wheels and moved forward by the same electro-magnet, which operates 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#