_Example._—September 10, 1910 (7th Month), Epact for 1910 being xix. 10 + 19 + 7 = 36. The Moon was 6 days old. What will be the date of full moon, its fifteenth day, in November 1912? November is the ninth month and the Epact for 1912 is xi. 11 + 9 = 20. 45 (= 30 + 15) - 20 = 25. _Ans._ November 17. Agriculturists who believe that certain seeds should be sown, trees planted, and pigs converted into bacon during the waxing of the moon, while trees are felled during the waning, find the Epact useful in reckoning the moon’s age. It is also useful in calculating whether country-roads will be moonlit during certain nights. The Epact increases 11 days annually: 1911, 0; 1912, xi; 1913, xxij; coming back to 0 in 31 years. _The Compass Card_ While the circle of the horizon is divided into 360 degrees for astronomy and for accurate navigation, the steersman has always divided it sexdecimally. The temple of the Winds at Athens was octagonal; and the points of the horizon were named after the eight winds, a number increased to sixteen about the time of Ptolemy. The Romans tried in vain to substitute an uncial division; their 12 winds and points could not supersede the 8 winds and points of the Greeks. And to this day in the Mediterranean there are 8 principal points, named after the sun and winds: Tramontano, Levant, Mezzodi, Ponente. Greco, N.E.; Scirocco, S.E.; Libeccio, S.W.; Maestralo, N.W. Amerigo Vespucci sailed for the ‘_Ponente una quarta di Libeccio_,’ West, one point S.W.; and afterwards for the ‘_Libeccio una quarta del Mezzodi_,’ S.W. one point S. [Illustration: DIAGRAM INDICATING THE PLANET RULING EACH HOUR, FROM DE TEMPORUM COMPUTATIONE ATQUE DIVISIONE, Joannis Padovanii, Veronæ, 1577. ] ------------------------------------------------------------------------ CHAPTER XV MEASURES OF HEAT AND OF DENSITY AND COMPOUND INDUSTRIAL UNITS 1. MEASURES OF HEAT _Thermometric Scales_ About 1595 Galileo made a thermometer, probably one with an air-bulb in which expansion of the air forces water down the tube. Isaac Newton made an oil-thermometer with a scale of 12° between freezing-point and body-heat. Fahrenheit, about 1714, made a mercurial thermometer, its 0 at the cold produced by a refrigerating mixture and 24° at body-heat. On this scale, freezing-point was 8° and boiling-point 53°. The quarter-degrees were then made whole degrees, producing the Fahrenheit scale with 32° for freezing-point, 96° (more correctly 98·4°) for body-heat, and 212° for boiling-point at ordinary atmospheric pressure. There are 180° between freezing and boiling points. Réaumur’s scale has 80° between these points.