There are various spells intended to be used to summon a person into the magician's presence but perhaps the most famous among modern magicians is that supplied by Charles Hether-Gray. It is this which Mr Segundus recommends to Jonathan Strange on the occasion when he accidentally spoils the latter's tête-á-tête with the late Miss Absalom. Our author tells us however that this kindly-meant advice is mistaken as, for all its fame, Hether-Gray's spell is quite useless.
On this occasion Mr Strange confides he has been successful in bringing Miss Absalom into his dreams by using a spell found in Ormskirk, but this triumph we must conclude is mostly due to his rare turn for magic, for we are told that other magicians have never succeeded by using Ormskirk. His success may however also be in part a result of the lady's gracious disposition, for we see when Mr Strange is struggling to summon the gentleman with the thistle-down hair how very difficult it can be to call up another and more experienced magician who simply does not wish to appear. The summoning part may be performed satisfactorily - but what use is that if the person summoned simply chuses not to be seen?
A similar difficulty arises when the two magicians together attempt to summon John Uskglass, using what is essentially Mr Strange's own spell, but rationalized and re-ordered by Mr Norrell. The spell succeeds, after a fashion. Uskglass briefly appears to them, but not in a form they immediately recognize, and he is not constrained to stay.
We are not told what spell Mr Norrell used when he first successfully summons the gentleman with the thistle-down hair[7,8].
As is widely known, a traditional English summoning spell contains three elements: the envoy (to find the person summoned); the path (to bring them to the summoner); and the handsel, or gift, (which binds the person summoned to come). On the occasion when Mr Strange and Mr Norrell had the honour to solicit the attendance of the Raven King himself, they were in Hurtfew Abbey, which had formerly been his Majesty's property. They therefore used the abbey stones as summoner, the nearby River Hurt as path, and the next-year's crop of fruit trees as handsel. And, as Mr Strange rightly observed, in addition to the above three items any successful summoning spell must also contain a temporal element, to convey to the person summoned exactly when he is meant to appear. On this occasion they used the lighted stub of a candle, and the moment of its extinction as the time for the King's appearance.
Quite why Jonathan Strange takes so roundabout a course when he evidently wishes to see Christopher Drawlight in Venice is not clear either. Clearly he lays some sort of enchantment on the waters of Venice so that they bring the wretched Drawlight into his presence as soon as it is feasible for them to do so; but why he does not summon Drawlight outright is less obvious. It may be he cannot be sure exactly which emissary Norrell and Lascelles are sending, and so his summoning spell has to be more general and inclusive in its nature than is usual - for precision, as Strange remarks earlier, is vital in spells of summoning.
see also A spell to summon a fairy