“COLUMBIA UNIVERSITY’S SPHERICAL SUNDIAL

By FOSTER WARE

Columbia University lays claim to the ownership of the only spherical sundial in the world. It is a ball, 7 ft. in diameter, and its shadow, falling upon a flat granite plinth, travels around the base and tells the time of day.

Prof. Harold Jacoby, head of Columbia’s astronomical department, has designed it so as to indicate standard New York time, not solar time as is ordinarily shown by sundials. These two kinds of time, of course, usually disagree, sometimes by a considerable fraction of an hour. Prof. Jacoby’s work consisted chiefly of calculating the angle of the ball’s shadow at noon for every day in the year.

With the sun shining, the big sphere casts an elliptical shadow, which travels around the base as the hours pass. It would be possible, of course, to add to the number of hour marks so that the dial would indicate time all day long, and this may be done when the necessary calculations have been completed. For the present, however, a series of 12 concentric circles—one for each month in the year—have been engraved upon a bronze plate inlaid on the surface of the base.

On each line are marks numbered to represent each day in the month. When the shadow intercepts a given line at one of these marks, it will be 12 o’clock noon of that particular day. The position of the shadow at noon is different every day of the year, so that it will touch a given mark—say August 1— only once a year at noon.

Prof. Jacoby has calculated the angles astronomically and believes that the dial will mark the noon hour to the exactness of a fraction of a minute. It is his opinion that, as the dial is more of an ornament and a curiosity than anything else, it will attract more attention and create more interest than a complete dial because the transit of the shadow each day at noon will bring together a considerable number of students and others tb watch the phenomenon.

The dial was recently presented to the university by the class of 1885, of which Prof. Jacoby is a member, as its quarter-centennial gift. It was erected at a cost of $10,000, and occupies a prominent place on the Columbia campus. The ball, which is made of polished green Ascutney granite, rests upon a broad flat granite base of neutral color. This base is 24 sided, and is decorated with inlaid bronze ornaments, designed by the firm of McKim, Mead & White, architects of the Columbia campus buildings. Many of the ornaments are taken from the signs of the Zodiac.”

Reference Data:

Popular Mechanics, Vol.14, Issues 1-3, 1910, page 356