This method of estimating longitude was, it is said, first discovered by noting that an eclipse which took place during the battle of Arbela was observed at Alexandria an hour later. If the time at which an instantaneous phenomenon such as an eclipse of the moon begins at Greenwich (or whatever be the first meridian) is known, and the time of its beginning at whatever place a ship is be then noted, the difference gives the longitude. The eclipses of the moons in Saturn have been used for the purpose. The method is not, however, a practically useful one. Owing to the penumbra it is difficult to observe the exact moment at which an eclipse of the moon begins. In certain positions of Saturn her satellites are not visible. Another method used was to note the lunar distances of certain stars, but the most common and practical method is by the use of well adjusted and carefully corrected chronometers giving Greenwich time. The comparison in the last five lines rests on a purely verbal basis. 'Longitude' means literally 'length', 'latitude', 'breadth'. Therefore longitude is compared with the duration of love, 'how long this love will be.' There is no real appropriateness. PAGE =33=. LOVES GROWTH. ll. 7-8. _But if this medicine, &c._ 'The quintessence then is a certain matter extracted from all things which Nature has produced, and from everything which has life corporeally in itself, a matter most subtly purged of all impurities and mortality, and separated from all the elements. From this it is evident that the quintessence is, so to say, a nature, a force, a virtue, and a medicine, once shut up within things but now free from any domicile and from all outward incorporation. The same is also the colour, the life, the properties of things.... Now the fact _that this quintessence cures all diseases_ does not arise from temperature, but from an innate property, namely its great cleanliness and purity, by which, after a wonderful manner, it alters the body into its own purity, and entirely changes it.... When therefore the quintessence is separated from that which is not the quintessence, as the soul from its body, and itself is taken into the body, what infirmity is able to withstand this so noble, pure, and powerful nature, or to take away our life save death, which being predestined separates our soul and body, as we teach in our treatise on Life and Death. But by whatsoever method it takes place, the quintessence should not be extracted by the mixture or the addition of incongruous matters; but the element of the quintessence must be extracted from a separated body, and in like manner by that separated body which is extracted.' Paracelsus, _The Fourth Book of the Archidoxies. Concerning the Quintessence_.