174 KANSAS CITY REVIEW OF SCIENCE. 
The very fact that human ingenuity has evoked from chaos this gigantic 
combination of forces, which is now causing the world of trade to tremble be- 
neath its ponderous tread, is itself an assurance that human genius will also teach 
us how to curb this embodiment of concentrated power, and train it to work 
quietly in the service of commerce. 
Jefferson City, Mo., June i, 1883. 
ASTRONOMY. 
TIME OBSERVATIONS. 
W. W. ALEXANDER. 
The correct measurement of time is not only one of the most important parts 
of practical astronomy, but it is one of the most direct benefits conferred on man- 
kind by the science ; it enters, in fact, so much into every affair of life, that we are 
apt to forget there was a period when that measurement was all but impossible. 
Among the contrivances which were to the ancients what clocks and watches 
are to us, may be mentioned the clepsydrge, or water clocks, sun-dial, hour-glass, 
etc. About the year 780, B. C, clepsydrae of the most elaborate construction 
were common ; but while they were in use, the days, both in summer and winter, 
were divided into twelve hours, from sunrise to sunset, and consequently the hours 
in winter were shorter than in summer. The clepsydra, therefore, was almost 
useless, except for measuring intervals of time, unless different ones were em- 
ployed at different seasons of the year. 
The sun-dial also is of great antiquity, being referred to as in use among the 
Jews 730 B. C. This was a great improvement upon the clepsydra, but at night 
and in cloudy weather it could not be used of course. To understand the con- 
struction of a sun-dial, let us imagine a transparent cylinder having an opaque 
axis; both axis and cylinder being placed parallel to the axis of the earth. If 
the cylinder be exposed to the Sun, the shadow of the axis will be thrown on the 
side of the cylinder away from the Sun, and as the Sun appears to travel round 
the earth's axis in twenty-four hours, it will equally appear to travel round the 
axis of the cylinder in the same time, and will cast the shadow of the cylinder's 
axis on the side of the cylinder as long as it remains above the horizon. 
All we have to do, therefore, is to trace on the side of the cylinder twenty- 
four lines fifteen degrees apart (15X24 — 360), taking care to have one line on the 
north side. When the Sun is south at noon, the shadow of the axis will be 
thrown on this line, which we may mark XII ; when the Sun has advanced 
one hour to the west the shadow will be thrown on the next line to the east. 
