A NEW CHRONOGRAPH. 573 
ASTRONOMY. 
A NEW CHRONOGRAPH. 
BY THE EDITOR. 
Mr. W. W. Alexander, of this city, has in use a chronograph, of his own 
design and construction, by the use of which he is enabled to determine the time 
of a star’s passage across the meridian, or, more exactly, across the five vertical 
wires of his transit, and to note the time the star is bisected by the wire, to the 
tenth or the hundreth part of a second by merely pressing a spring. 
The principle is as follows: A round disk of paper, placed upon a horizontal 
block of wood four inches in diameter, is made by accurately running clock-work 
to turn around once in a minute of sidereal time, or nearly so, (a slight variation 
may be corrected). A needle point is arranged at a short distance above the 
moving disk, which simultaneously with the pressing of the spring, makes a hole 
_ in the paper and readjusts itself in position in less than the hundredth part of a 
second. At each round of the disk, the needle point moves in toward the center 
of the paper the sixteenth part of an inch, which prevents confusion in distin- 
guishing the punches. To illustrate its use, take the following example: 
Suppose an occultation of a star by the moon, or an eclipse (the time of which 
is desired to be known) takes place at about 8 h. and 5m. ‘Then at five or ten 
minutes before that time, arrange and place the disk of paperin position and start 
the Chronograph running; then observe by a standard clock or chronometer 
the end or beginning of some exact minute; then touch the spring, which marks 
the paper; then go to where the observation is to be made, and simultaneously 
with the occurrence again press the spring, and another mark is left on the paper 
disk. Then remove the disk and place it on the reading dial, which will show, 
by the relative positions of the marks, the interval from the time of the first mark 
made to the one made at the time to be noted, to the tenth or one hundredth of 
asecond. In this case suppose it showed 4 m. 12.7 s.; add this to the time of 
the first mark, 8 h. 1 m., which gives 8h. 5 m. 12.7 s., the time by clock or 
chronometer at which the occurrence took place. Then by knowing the error of 
the clock or chronometer, from previous observations with the chronograph and 
transit, the observation may be made exactly correct, in time, by adding or sub- 
tracting this difference (ze. aside from personal equation). 
Another feature in its favor is this, that the marks on the disk are permanent, 
and can be preserved and read at leisure, thus obviating the necessity of using 
bright lights for night work and careful scrutiny of delicate lines and points at 
the instant of observation. 
Mr. Alexander is a close and careful observer, and invented this instrument 
merely for his own use and convenience, but on account of its simplicity, dura- 
bility and accuracy, it will doubtless be found so highly useful as to be speedily 
adopted by other astronomers. 
