William Gilbert’s date of birth has been difficult to establish. There are no known surviving family records, and the parish records covering the time of his birth in Antigua have been lost. The original DNB article published in 1901 estimated 1760 for his year of birth. 1760 can be ruled out as too early, because the Gilbert family tree in Oliver’s History of the Island of Antigua shows 1761 as the year of birth for William’s elder brother Nathaniel.  Unfortunately the actual day is not given, but the year of birth is likely to have been obtained from descendants – Oliver was assiduous in tracing genealogy of the Antigua families for his history, and adds a question mark to any doubtful date. Thus, when it comes to William for whom information was not available, he puts him as a child born after Nathaniel, but gives no dates at all. If Nathaniel’s year of birth is right, the earliest year for William’s birth would be 1762, and given his known career dates (December 1783: appointed Clerk to the Antigua House of Assembly) the earliest possible date would be most likely.
When I first read Gilbert's words in the July 1793 Conjuror's Magazine that, ‘my person certainly met the description of Mars in Virgo and Mercury in Scorpio’, I looked up astrological ephemeris tables and established that there were two possible date windows when these planets were in the right signs: 13 October - 3 November 1761, and 30 September - 9 November 1763. I felt the earlier date was the likeliest option, and speculated that if his brother had been born very early in 1761 - say 1 January - it was biologically feasible, if a bit hard on his mother, for William to be born ten months later. But, after working back carefully over the entire sequence of articles published by Gilbert and others in the Conjuror’s Magazine, and paying better attention to the astrological charts, I now believe enough evidence exists to show that he was born on 1 October 1763.
Gilbert, a regular contributor on magic and astrology under the name B. publishes an astrological query under the name of ‘Omega’. He prints two conjoined astrological charts, but does not disclose the dates of birth of the two subjects, putting this double horoscope forward as a blind test for astrologers, as if it is purely a matter of theory. The challenge is to deduce from these given horoscopes what injuries each has had in infancy, what sex each is, what attributes, their marriage prospects, and what ‘sympathies’ lie ‘between the two’.
Five months later under his normal pseudonym of B., Gilbert acknowledges the query as his, and says that he has not had any response to it. He then names and challenges another astrologer W. E. (William Elder) to answer his questions. He refers to a consultation and disagreement with Elder who ‘insists that Leo on the ascendant will not describe the person of No. 2, and takes Virgo and Mars’. I believe that No. 2 is Gilbert himself, because of the terms of the argument between Gilbert and Elder over the time of birth. Elder wanted to rectify No. 2’s horoscope by adjusting the time of birth. This rectification is a major skill required of an astrologer. The ascendant – i.e. the sign and degree rising over the horizon at the exact time of birth - is a vital part of the horoscope, and because the precise time was seldom known, the astrologer needed to work backwards from known events, character and appearance of the person, to arrive at a rectified or adjusted moment of birth that fitted these known facts.
Elder responds to Gilbert’s challenge by setting out his case: working from the configuration provided and looking up his tables he can identify No. 2’s birth date. The combined position of the slow-moving outer planets Saturn and Jupiter will establish the year of birth; the Sun’s position will provide a day of the year, the moon’s position can be used to determine the approximate time, and the sign and degree of the ascendant will give an exact moment. Elder arrives at 1 October 1763. But he does not disclose the place of birth, which is essential to the calculation. He disputes the given time of birth because in his opinion the physical appearance of person 2 does not correspond to Leo 19° ascendant, and he accordingly wants to rectify:
The gentleman whose nativity this is, ought to be of a fine clear complexion, with auburn brown hair. But only mark well the malice and partiality of his ill-natured stars; for instead of what we have now described him to be, he is of a dull, swarthy, sallow complexion, with very dark hair and eyes. I shall, for these reason, take the liberty of making the time of birth an hour and forty minutes later, and we shall then have five degrees of Virgo ascending, and Mars exactly on the cusp of the ascendant […]
This shows that Elder knows the appearance of this person, and there is something gratuitously malicious in his description. He continues to fault Gilbert’s astrology in subsequent articles with similar malice: ‘should I hear that any person was so much out of himself as to follow this absurd rule, I should immediately conceive he was almost fit for the strait jacket.’ Elder wins this pecker contest: he gains ascendancy in the Magazine, and the defeated Gilbert disappears from view. The editor remarks, ‘What is become of Mr. B.? Has W. E. touched him too closely?’
Gilbert does not reappear in the pages of the Magazine until March 1793. In July 1793 (a fourteen-month interval) he returns to his old disagreement with Elder during a discussion about his own ascendant:
Now, whether Leo 19 deg, and some minutes, be my ascendant or not; if I have met with one question of enemies on marriage, where Aquarius 19 deg. either ascended or had Mars or some distinguished planet on it, I aver, that I have met with fifty. Mine is the only birth where my father has put minutes down; he was curious in keeping time, for, exclusive of a stone dial affixed to the house, he kept a ring dial, whereby he often regulated […] What W. E. said, had, however, great weight with me, because my person certainly met the description of Mars in Virgo and Mercury in Scorpio.
Gilbert has asked for advice regarding a horoscope that he has presented in a very hidden way. He and Elder have disputed the time of birth. When he returns to the argument his main point is that his time of birth had been meticulously recorded by his father, but Elder was right to say that his personal appearance met Elder’s description. The likeliest scenario is that Gilbert went to Elder for a consultation about his own horoscope and had a disagreement when Elder wanted to rectify his time of birth. Gilbert had his own reasons for believing he had Leo 19° ascendant. So he published his chart (disguised as much as possible to protect his identity) in November 1791 in order to get astrological support for his side of the argument. Elder’s argument from astrology was plausible but Gilbert knew that his father’s time keeping was reliable. A ring dial is a device for recording time.
The horoscope provided by Gilbert can be replicated near enough with modern tables. See detailed data. The signs are favourable - Gilbert's placement of the Mid-heaven is appropriate for the latitude of Antigua as a place of birth, but not for England. There is also a strange remark by Elder that suggests a birthplace in that latitude : ‘I think it would not be amiss to ask Mr. B. how we are to proceed in forming the description of the native, when the beginning of Cancer ascends in this latitude’. Antigua’s latitude is close to the Tropic of Cancer – a point made later by Gilbert when in the first line of The Hurricane he writes that Antigua lies ‘Near where with Tropic heats bright CANCER glows’.
One problem remains: Elder’s stated time of birth,10:30 a.m. It can’t be the local time of birth because it doesn’t match the position of the sun (about three hours fifteen minutes before dawn). If we assume Elders means 10:30 a.m. English time, the time in Antigua would still not fit the sun’s position. The local time of this horoscope which fits for Antigua is approximately 2:30 a.m., and this 8 hour difference can only be fulfilled at a longitude of 120° West which at this latitude is far out in the Pacific Ocean. This is a mystery, but it does not point to any alternative birth date.
Another piece of corroboration is the obscure reference to a person with the rising sign of Leo ‘scarcely distinguished at all, and that little, by POVERTY’ in his article on the solar eclipse of 1788 (see note E4). It is hard to explain the point of this obscure little reference unless it is about himself.
This date of birth, 1 October 1763, is about a year later than would be expected, but it is feasible and — if right — it means that Gilbert’s career was precocious. He was chosen at the age of 22 by an Army Officer seeking legal assistance for a Court Martial. This either speaks highly of his abilities, or of the undesirability of the task. The officer concerned was unpopular with his regiment and with the Antiguans. The fact that John Henderson, Gilbert’s carer or companion at the Hanham Asylum in 1788, referred to him as the ‘young counsellor’ backs up this sense of early advancement.