This series of 135 lunar months, or 23 eclipse seasons, can be repeated almost indefinitely, alternating 3986 and 3987 days to the series and still keep the synodical month in accord with the eclipse season. But another factor must also be considered. Months of 29 and 30 days cannot be simply alternated and either conform with the true synodical month or complete the ecliptic series mentioned, for 3986 contains three more days than sixty-eight 30-day months, and sixty-seven 29-day months. Therefore in the 3986 series three of the 29-day months must be changed to 30-day months, and in the 3987 series four must be changed. The position of these changes is arbitrary. They can, for example, be the 34th, 68th, and 102d months, and when necessary, the 134th. TABLE IX COMPARISON OF SYNODIC MONTHS AND ECLIPSES Eclipse season Synodic month Number Days Number Days Difference 1 173.310 6 177.184 3.874 2 346.620 12 354.367 7.747 3 519.930 18 531.551 11.621 4 693.240 23 679.204 -14.036 5 866.550 29 856.387 -10.163 6 1039.860 35 1033.571 -6.289 7 1213.170 41 1210.754 -2.416 8 1386.480 47 1387.938 1.458 9 1559.790 53 1565.121 5.331 10 1733.100 59 1742.305 9.205 11 1906.411 65 1919.489 13.078 12 2079.721 70 2067.141 -12.580 13 2253.031 76 2244.325 -8.706 14 2426.341 82 2421.508 -4.833 15 2599.651 88 2598.692 -.959 16 2772.961 94 2775.875 2.914 17 2946.271 100 2953.059 6.788 18 3119.581 106 3130.243 10.662 19 3292.891 112 3307.426 14.535 20 3466.201 117 3455.079 -11.122 21 3639.511 123 3632.263 -7.248 22 3812.821 129 3809.446 -3.375 23 3986.131 135 3986.630 .499 TABLE X 148-DAY GROUPS