OF DIALING. 391 



Babylonian day. But we are not thence to imagine that LECT. 

 the equal hours, which it shews, were those in which ^x^v^x. 

 the astronomers of that country marked their observa- 

 tions. These, we know with certainty, were unequal, 

 like the Jewish, as being twelfth parts of the natural 

 day : and an hour of the night was, in like manner, a 

 twelfth part of the night ; longer or shorter, according 

 to the season of the year. So that an hour of the day, 

 and an hour of the night, at the same place, would 

 always make ^ of 24, or 2 equinoctial hours. In Pales- 

 tine, among the Romans, and in several other countries, 

 3 of these unequal nocturnal hours were a vigilia or 

 watch. And the reduction of equal and unequal hours 

 into one another, is extremely easy. If, for instance, 

 it is found, by a foregoing rule, that in a certain lati- 

 tude, at a given time of the year, the length of a day is 

 14 equinoctial hours, the unequal hour is then li or J of 

 an hour, that is, 70 minutes ; and the nocturnal hour is 

 50 minutes. The first watch begins at VII (sun-set;) 

 the second at three times 50 minutes after, viz. IX h. 

 30 in. the third always at midnight ; the morning watch 

 at ; hour past II. 



If it were required to draw a dial for shewing these 

 unequal hours, or 12th parts of the day, we must take 

 as many declinations of the sun as are thought neces- 

 sary, from the equator towards each tropic : and having 

 computed the sun's altitude and azimuth for ^, , ^ 

 parts, &c. of each of the diurnal arcs belonging to the 

 declinations assumed : by these, the several points in 

 the circles of declination, where the shadow of the stile's 

 point falls, are determined : and curve lines drawn 

 through the points of an homologous division will be 

 the hour-lines required. 



Of the right placing of Dials, and having a true meridian 

 line for the regulating of clocks and watches. 



The plane on which the dial is to rest, being duly 



