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Sundials: Sundial Hour Lines

The following pages tell how to lay out the hour lines for many kinds of sundials. It would be impossible to show the construction of all kinds and fortunately it is not necessary to do so. The kinds shown have been selected with care in order to provide the information for making as many types of sundials as possible by adapting the principles of one to the other. For example it is easy to make a cross sundial by applying the principle of the armillary or equatorial.

1. The construction of the hour lines
2. How the sundial plate should look when completed
3. The proper position for the sundial when in use.

The supplementary text gives first the important parts of each sundial that must be known or found, before the hour lines can be laid out. Then follows the construction of the lines, the hour limitations or the number of hour lines necessary to be shown, and lastly how to set the sundial. In some instances, such as for the declining sundial, a general note has been added at the end whenever necessary to make the work easier or as a guide in making other sundials of similar character.

The names for each kind of sundial are given in accordance with general usage. We start by showing the construction of one of the simplest forms of all and the easiest to construct, the equatorial sundial.

THE EQUATORIAL SUNDIAL
The equatorial sundial is one of the simplest forms of the sundial and one of the easiest to construct. The plane of this sundial lies parallel to the plane of the equator and it can be used at any place on the earth, provided the style is inclined at an angle above the horizon equal to the latitude of the place in which it is to be used. The STYLE is a round rod, which passes through the sundial plate and is perpendicular to it. It points to the celestial pole. The SUBSTYLE is the center of the sundial, at point E. The HEIGHT OF THE STYLE is determined by the size of the sundial plate, and is usually from 6 to 8 inches high. The Construction Fig. r With E as a center, describe a small circle whose diameter is equal to the diameter of the style. Also, with E as a center, describe the circle ABCD. Draw EB, for the meridian; then draw the line 12 for the 12 o'clock line, parallel to EB and tangent to the small circle representing the diameter of the style.

Divide the circle ABCD into 24 equal parts, beginning at the point 12; and from the points thus found draw lines tangent to the small circle and on the same side.. These lines will be the required hour lines. When the style has been erected perpendicular to the sundial plate the hour will be shown by the left-hand edge of the shadow. Note: If the style is less than 1/8" in diameter, or if the rod tapers to a point at the top, all the hour lines will be drawn from the center, at E; and the division of the hours will begin at the point B. This sundial will show the time from sunrise to sunset throughout the year, if the hour lines are inscribed on both faces of the plate. Otherwise the sundial will show only the time during the six months of summer, between the Equinoxes.

Setting the Sundial
An equatorial sundial must be so placed that the style points to the celestial pole, which will be at an angle above the horizon equal to the latitude of the place. The plane of the sundial must be perpendicular to the style, and the 12 o'clock line must lie in the plane of the meridian.

THE HORIZONTAL SUNDIAL
The horizontal sundial is the most common type of sundial. Its plane lies parallel to the plane of the horizon. The diagram shows the construction of the hour lines for latitude 430 N. The STYLE points to the celestial pole. The SUBSTYLE is the 12 o'clock line and lies in the plane of the meridian. The HEIGHT OF THE STYLE is equal to the latitude of the place (43010' in the example). Draw the horizontal line FAG (This will be the 6 o'clock line). At A, draw AC perpendicular to FAG (This will be the 12 o'clock line). Draw AD so that the angle DAC is equal to the latitude of the place (In this case 43°'). From B, on AC, draw BE perpendicular to DA. Make BC equal to BE; then make AG and AF equal to AC. Draw lines FC and CG. Through B draw a line parallel to FG, cutting CG at M, and FC at L.

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