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 6

They also divided the year into twelve parts, devised the week of seven days, and foretold eclipses. One of the simplest forms of the sundial; the hemispherium,

Figure 4 is attributed to the Chaldean priest and astronomer, Berosus, who lived at the time of Alexander the Great (356-323 B.C.). This sundial was carved out of a block of stone, its concave hemisphere resembling the inverted vault of the heavens. A perpendicular pin or style was placed in the center, pointing to the zenith; then as the sun traversed the sky, the shadow of the top of the pin would trace out the apparent motion of the sun in a reverse direction. That portion of the inner surface upon which the sun shone was divided into twelve parts representing the temporary hours. The hour lines were crossed by three or seven other lines cor- responding to the seasons or months, which were determined by the same method used in Egypt. Although inaccurate, the hemispherium was far superior to the waterclocks in common use at the same time, because they were bulky, needed attention and could not be carried about easily; whereas the hemispherium could be made small enough to be carried in the pocket and set up anywhere. The hemicyclium, Figure g, is also attributed to Berosus and it is often referred to as the "sundial of Berosus." There is a difference of opinion concerning the inventor of these two sundials which may be due to a loose use of the two words in modern literature as meaning the same kind of sundial. Although there is no difference in the construction of the lines, the hemicyclium has the front or south portion cut away at an angle, and a horizontal gnomon is used instead of a perpendicular one. The portion cut away is useless for time-keeping purposes because the shadow would never enter that part. Some early writers considered the hemicyclium a great improvement over the hemispherium, which was probably due to the greater ease in reading, and its lighter weight. Both sundials were made in forms and sizes too numerous to mention.

  more on the development of the sundial...