Page:A short history of astronomy(1898).djvu/61

§ 16] annual journey, being never more than about 47° and 29° respectively distant from it, on either side; while the other planets are not thus restricted in their motions.

16. One of the purposes to which applications of astronomical knowledge was first applied was to the measurement of time. As the alternate appearance and disappearance of the sun, bringing with it light and heat, is the most obvious of astronomical facts, so the day is



the simplest unit of time. Some of the early civilised nations divided the time from sunrise to sunset and also the night each into 12 equal hours. According to this arrangement a day-hour was in summer longer than a