This map, which contains the twelve divisions already described as the twelve houses of heaven, may be drawn in either a square or circular form. Lilly and other mediæval writers use both forms indiscriminately; but as the latter is more easily understood, the diagram (plate 2) is drawn up in that manner. It will be seen that it is formed of three circles. In the centre space the date, time and place of the event of a horary question are entered, and in a nativity the name, sex and moment of birth of the native. The next space (divided into twelve equal parts for the houses) is reserved for the planets and in the outer space are placed the signs of the zodiac, with the number of their degrees, on the cusp of each house. The cusps of the Houses are represented by that line between each house. Having obtained an Ephemeris, or astrological almanack[ [7] for the year required, we must find the Sidereal Time for the day and month of the birth, or question; then, if the time of the event be before noon we must deduct the difference between the given time and noon from the Sidereal Time of the day; for example, on the day of the event (the 9th January, 1889), the Sidereal Time at noon is shown by the Ephemeris to be 19 hours 16 minutes 51 seconds, if the birth had been at 9 a.m. The difference between 9 a.m. and noon is 3 hours. We should, therefore, have to deduct 3 hours from 19 hours 16 minutes 51 seconds, which gives 16 hours 16 minutes 51 seconds, the Sidereal Time required.
As the event is supposed to happen at 3 in the afternoon, we must add the difference between noon and the time given to the Sidereal Time of the day. The difference between noon and 3 p.m. is 3 hours, and, as the Sidereal Time on the 9th January, 1889, is 19 hours 16 minutes 51 seconds, we add 3 hours to this amount, which gives 22 hours 16 minutes 51 seconds, the Sidereal Time required.
We must now proceed to place the signs for 3 p.m. on the 9th January, 1889, which is thus done: We turn to the "Table of Houses" (which will be found at the end of the Ephemeris), and having found (under the column headed "Sidereal Time") the nearest time to 22 hours 16 minutes 51 seconds, which in this case is 22 hours 16 minutes 48 seconds for the latitude of London, we see in the next column (headed 10) the sign
(Pisces), and the number 3° opposite our Sidereal Time, showing that the third degree of Pisces is on the cusp of the 10th house, In the next column (headed 11) we see
, and the number 7°; we therefore place 7°
on the cusp of the 11th house, next 24°
