SUNDIAL SECTIONS:

Sundials Home

History of Sundials

Why the Sun Dial keeps time

Developing and Making Sundials

Sundial Materials

Sundial Hour Lines Lay out

Sundial "Furniture"

Declination Lines of Sundials

Portable Sundials

Interesting Sundials of the World

DEVELOPMENT OF THE SUNDIAL - PAGE 4

Such a sundial if made small and light enough, could easily be carried about. One more Egyptian sundial,

Figure 3, is of particular interest. It is of the period about 330-30 B.C. (Hellenistic Period), and shows a decided advance over the previous sundials in that instead of a horizontal surface to record the position of the shadow cast by the upper edge of a perpendicular block or gnomon, the surface was inclined at an angle equal to the latitude of the place. Its width was divided to show the months and across these divisions diagonal lines were drawn representing the hours of the day. When in use the instrument was first placed in a level position by means of the plumb line, then turned so that the perpendicular block was pointed directly toward the sun. The position of the shadow upon the hour lines corresponding to the proper month would show the time for any day. This was an ingenious device, because the Egyptians did not make use of hours of equal length, as we do today; they used temporary or unequal hours. Temporary hours resulted from the division of the period between sunrise and sunset into twelve equal parts. Because the length of this period varies throughout the year, it was not possible to obtain equal divisions of time by such a method except on any one specified day. Therefore it was necessary to observe the position of the shadow at each hour on several days during the year, preferably at the time of the equinoxes and the summer and winter solstices. If lines drawn through these points were crossed by others designating the months the true temporary time could thus be obtained any day in the year. Timekeeping was not the only incentive for making these sundials, for they were often used as votive offerings and placed in temples, in a sundial area.

  more on the development of the sundial...