ASTRONOMY IN SHAKESPEARE'S TIME— ABBOT H'J 



For instance, by observing the length of the shadow of a vertical rod 

 on a horizontal floor, noon would be indicated each day as the in- 

 stant of the day's shortest shadow. Soon a mark could be made to 

 indicate the direction of the shadow at every noon, and this would 

 be the line of north and south. Presently it would appear that the 

 end of the shadow at noon marched southward from July to Decem- 

 ber and then returned. A diligent observer, watching this march of 

 the end of the noon shadow for several seasons, would obtain a more 

 and more accurate measure of the length of the year. As long ago 

 as the times of the ancient Chaldeans and Egyptians the year was 

 thus known to be about 3651/4 days. If shadow observations were 

 continued over centuries, as doubtless they were by priests as re- 

 ligious rites, the fraction approximately one-fourth could be deter- 

 mined to several decimals. 



From the total length of the excursion of the shadow's end be- 

 tween June and December, compared to the height of the rod which 

 cast it, the angular inclination of the ecliptic to the Equator was 

 determined several centures before Christ as 2314°. Eratosthenes, 

 about two centuries before Christ, went further. He observed that 

 the sun at midday in Alexandria at the summer solstice stood V^q 

 of a circumference, or about 7° from the zenith, whereas at Syene, 

 in Upper Egypt, the sun at the same time stood exactly overhead. 

 From this he inferred that the distance from Alexandria to Syene 

 was 1/^0 of the circumference of the earth. His observation agrees 

 closely with the truth. Another use of the march of the end of the 

 sun's shadow from north to south would discover the dates at which 

 it stood exactly half accomplished. These dates, corresponding to 

 the equinoxes, would reveal the inequalities of several days which 

 we now attribute to the ellipticity of the earth's orbit round the sun. 

 Latitudes were also readily determined by the ancients from the 

 direction and length of the sun's shadow. 



But enough ! We will not follow the shadow farther but turn 

 our attention to the astrolabe, the pearl of ancient instruments. 

 Imagine, if you please, that your watch was expanded in diameter 

 several fold, and that its chain ended in a loop large enough to hang 

 on the thumb or finger instead of in a bar or hook. Assume the 

 weiglit of the watch increased to 1 or 2 pounds, its glass and 

 works removed. On the face, instead of hands, would be pivoted 

 a bar carrying peephole sights at either end, by means of which 

 the axis of the bar could be pointed at the sun, a star, or at some 

 terrestrial object. Corresponding to the position of the hours. III 

 and IX of the watch would be the horizon line. The angle be- 

 tween the sighting bar and the horizon line could be read off on 

 the graduated circle. Sighting through such an instrument, held 



