In the present state of astronomical science it is not certain that these values are absolutely correct. Calculated from the Tables of Kepler, the differences are only slight, but still sufficient to make considerable error in testing for exact conjunctions or ingresses. Lilly, who predicted the Great Plague and Fire of London some years previous to the event from the ingress of the Aphelion of Mars to the sign Virgo, evidently made use of the Rudolphine Tables constructed by Tycho and Kepler, and according to these the ingress took place in 1654, while according to more modern Tables it did not take place until 1672. It is probable, however, that the positions of the Aphelia here given will be sufficiently close for all practical purposes. A word or two may now be said regarding the periodic conjunctions of the planets. As will be seen from the periods given, five periods of Jupiter are nearly equal to two of Saturn. It is found that the two planets form their conjunctions every 20 years. Thus there was a conjunction in Virgo in 1861, another in Taurus in 1881, and another in Capricornus in 1901. The next will be in Virgo in 1921. The two planets are thus now forming their successive conjunctions in the Earthly Tripicity; but in 1981 will make their mutation conjunction by falling together in the Airy sign Libra. Uranus and Jupiter form their conjunctions every 14 years. Thus there was a conjunction in Sagittarius in 1900, and there will be another in Aquarius in 1914, another in Aries in 1928, and so on. The conjunctions of Neptune with the other major planets are necessarily in terms of the periods of the latter, those of Neptune and Uranus being very infrequent, while those with Jupiter will be proportionately more frequent. For the period of Jupiter is only 12 years, while Neptune remains in the same sign for 15 years. The conjunction of Jupiter and Neptune in Cancer in 1907 will be followed by another in Leo in 1919, and this again by another in Virgo in 1932. Obviously, if the planets by their transits effect anything whatsoever, the double transit of major planets must have a correspondingly greater effect. The careful student of Astrology will institute a number of tests in order to find what effects are due to the combined action of the planets when in conjunction at transit, and also when in opposition or quadrature. The chief points to be noticed in connection with the transits of the planets are the Midheaven, Ascendant, and the places of the Sun and Moon, as already mentioned in Chapter II of this section. The ancients also included the places of the Moon’s Nodes, and it is usually found that the transit of the South Node over any of the Significators is attended by unfortunate results.