The magic-user acquires books containing the spells, the study of which allows him to memorize a spell for use. He can then throw the spell by saying the magic words and making gestures with his hands. This means that a magic-user bound and gagged can not use his magic. In some cases the spell may require substances or apparatus, such as conjuring a water elemental (5th level) requires the presence of water, a sleep spell requires a pinch of sand. A magic-user must concentrate on his spell, so he can not cast a spell and walk or run at the same time, and he certainly can not cast a spell while engaged in combat. Then, after all that, the spell may not work!There's lots of information to digest in this paragraph. I'll begin only by noting that I'm personally amused by the appearance of the verb "throw" in reference to casting spells, a usage I see a lot in earlier gaming materials but that seems to have been superseded (The same usage also occurs in reference to dice too).
Holmes elaborates greatly on the in-game mechanics of magic, noting that spells require what AD&D calls "verbal" and "somatic" components to function. I wonder, given this and his reference to a bound and gagged magic-user, if this wasn't the beginning of the notion that the 2nd-level cleric spell, silence 15' radius, could be used as an offensive spell to shut down enemy spellcasters. Holmes notes too that some spells require "material" components, but, despite his examples, the descriptions for spells introduced later make no mention of material components. The requirement for absolute concentration is one that I've retained all these years and has colored my vision of how magic operates. His reference to spells not working "while engaged in combat" must be read with reference to the note about concentration: a magic-user actively fighting, as opposed to casting spells from a safe distance, lacks the focus needed to work magic.
Spell memorization is fleshed out slightly. The text notes that "as the spell is recited it fades from the spell-caster's mind and he can not use it again!" Re-memorization "takes at least 1 day" and, for unexplained reasons, "Magic-users can not bring their magic books into the dungeon with them." As a younger person, I took this to mean that spell books were tomes of immense size and weight, since spells were complex formulas, but Holmes nowhere explains his meaning.
Perhaps one of the best-known idiosyncrasies of the Holmes rulebook is its rules for scroll use and creation. Under these rules, magic-users of any level can make scrolls of spells they already know at a cost of 100 gp per spell level and 1 week's work, a rule I've used for years and that I allow in my Dwimmermount campaign. As Jeff notes, scrolls are specifically usable only by magic-users in Holmes, which raises some issues I'll discuss in a later post in this series. Spell research is also possible for magic-users, at a cost of 2000 gold piece per level of the spell and one week time, seemingly regardless of level. This expenditure grants a mere 20% chance of success, however, so researching even a new 1st-level spell may take much gold and many weeks. The level of any new spell under research is determined by the referee, of course, as with so much in Holmes.
Holmes includes Supplement I's "Chance to Know Any Given Spell" table based on the magic-user's Intelligence score. He also includes an actual explanation for how the table works, which is nice, since the Greyhawk table is quite mysterious on its own. I'll admit that I've always liked this table, as it gives magic a weird quality to it. There are some spells that are simply impenetrable to a given character and no amount of trying will enable his mind to grasp them.
Holmes uses the same saving throw categories as the LBBs, more or less, although his wand category doesn't explicitly include "polymorph and paralization [sic]" as OD&D does. They are, however, in a different order. Except for the fact that he groups thieves with fighting men rather than magic-users as in OD&D, the tables are functionally identical to those in the LBBs. Monsters are treated as fighting men of equal level in most cases, except for those whose magic use suggests they ought to be treated as either magic-users or clerics. Holmes also alludes to the existence of magic resistance for "large and powerful creatures like demons, balrogs and dragons." He also reiterates the traditional resistances of undead beings to sleep and charm type spells.