Fig. 12
[Fig. 12] represents what I call the trough-shaped dial. It is made of metal-plate bent into the shape of a half-tube; the ends are closed with semicircular metal plates. The interior is divided into twelve equal parts by lines running parallel to the edges, and are numbered from 6 to 6. A wire is stretched from the centres of the semicircular end plates to serve for the style.
This dial must be fixed, with regard to the position and direction of the style, as the other dials are. This is the one constant condition of all dials, that the edge of the style that is to cast the shadow must be parallel to the axis of the earth.
Fig. 13
[Fig. 13] is a very simple dial, and is the last I shall describe. It consists of a circular dial-plate divided into twenty-four equal parts, numbered from 1 to 12 twice over. The style is a perpendicular wire fixed in the centre of the plate. The plate is hinged to a stand, so that one of the twelve-o’clock lines runs directly from the top to the bottom.
From the construction of the [dials 10], [11], [12], [13], they can be used in any latitude, as well as on the equator, but of course the numbering would have to be reversed for the southern hemisphere. They all have an arrangement by which the style can be fixed at the required angle to suit the latitude of the place.
TABLE OF MINUTES.
To be Added to or Subtracted from the Sundial for each Day in the Year.
The sun does not always point out the true time, as on some days it is behind time and sometimes before it. The table below gives the minutes to be added to or subtracted from the time pointed out by the sun for each day in the year:—
| January. | ||
|---|---|---|
| Day. | Min. | |
| 1 | + | 4 |
| 4 | + | 5 |
| 6 | + | 6 |
| 8 | + | 7 |
| 11 | + | 8 |
| 13 | + | 9 |
| 16 | + | 10 |
| 19 | + | 11 |
| 23 | + | 12 |
| 27 | + | 13 |
| 31 | + | 14 |
| February. | ||
| 3 | + | 14 |
| 19 | + | 14 |
| 26 | + | 13 |
| March. | ||
| 3 | + | 12 |
| 4 | + | 11 |
| 12 | + | 10 |
| 15 | + | 9 |
| 19 | + | 8 |
| 22 | + | 7 |
| 25 | + | 6 |
| 28 | + | 5 |
| April. | ||
| 1 | + | 4 |
| 4 | + | 3 |
| 8 | + | 2 |
| 12 | + | 1 |
| 19 | - | 1 |
| 25 | - | 2 |
| 30 | - | 3 |
| May. | ||
| 1 | - | 3 |
| 17 | - | 4 |
| 28 | - | 3 |
| June. | ||
| 4 | - | 2 |
| 10 | - | 1 |
| 19 | + | 1 |
| 24 | + | 2 |
| 29 | + | 3 |
| July. | ||
| 4 | + | 4 |
| 10 | + | 5 |
| 19 | + | 6 |
| August. | ||
| 1 | + | 6 |
| 11 | + | 5 |
| 16 | + | 4 |
| 21 | + | 3 |
| 25 | + | 2 |
| 29 | + | 1 |
| September. | ||
| 4 | - | 1 |
| 7 | - | 2 |
| 10 | - | 3 |
| 13 | - | 4 |
| 16 | - | 5 |
| 18 | - | 6 |
| 21 | - | 7 |
| 24 | - | 8 |
| 27 | - | 9 |
| 30 | - | 10 |
| October. | ||
| 3 | - | 11 |
| 7 | - | 12 |
| 10 | - | 13 |
| 14 | - | 14 |
| 19 | - | 15 |
| 27 | - | 16 |
| November. | ||
| 10 | - | 16 |
| 17 | - | 15 |
| 21 | - | 14 |
| 25 | - | 13 |
| 28 | - | 12 |
| December. | ||
| 1 | - | 11 |
| 2 | - | 10 |
| 6 | - | 9 |
| 8 | - | 8 |
| 10 | - | 7 |
| 12 | - | 6 |
| 14 | - | 5 |
| 16 | - | 4 |
| 18 | - | 3 |
| 21 | - | 2 |
| 23 | - | 1 |
| 27 | + | 1 |
| 29 | + | 2 |
| 31 | + | 3 |