Wizards, magicians, mages, magic-users; whatever the name for the class, they have long been the "blasters" of Dungeons & Dragons, deploying their spells to incapacitate, control, or detonate their enemies.
A casual perusal of the list of magic-user spells in the 1st edition AD&D Player's Handbook shows that there's an interesting omission in the second-level spell list: To wit, none of the spells of that level cause damage.
Of course, a canny magic-user has plenty to do with second-level spells. Invisibility is a prime staple, making it possible for the party's thief to move into backstabbing position unseen, or helping the magic-user to escape enemies while looking for a safer vantage point from which to deploy spells. Stinking cloud and web both have excellent area-control opportunities. Strength is a prime boosting spell for the party's fighters, while ray of enfeeblement can greatly reduce the effectiveness of enemy melee attacks. But none of the spells at that level cause damage directly.
Once Unearthed Arcana arrives, this changes with the addition of flaming sphere and Melf's acid arrow. Once again the magic-user's spells include damage-dealers and a humble 3rd- or 4th-level magic-user may continue to blast enemies with aplomb.
It's possible, of course, that this is simply an oddity of the spell structure. Low-level magicians are given spells like magic missile, burning hands, and shocking grasp as their bread-and-butter -- simple spells that deploy a small amount of damage. Mid-level magic-users gain the vaunted area of effect spells like fireball, lightning bolt, ice storm, and cone of cold. High-level magic-users simply rely on spells that kill foes outright. This makes the spell gap at the second level spell list seem all the more odd.
The other possibility is that this is a deliberate gap. Another artifact of the mad genius of the wizard of Greyhawk? Perhaps. The lack of any direct damage spells at the second-level spell list means that a magic-user who reaches 3rd level, and gains one of those spells, now must choose something beyond just blasting -- battlefield control (web or stinking cloud), boosting allies (strength or invisibility), neutralizing enemies (ray of enfeeblement or scare), or deploying defenses (mirror image or levitate). This is an interesting place to put such a gap. The magic-user has already learned to use a few spells to inflict damage and probably to perform some wide-ranging knockouts (sleep being a king of low-level spells). Now the magic-user must learn how to use more powerful spells in a context outside of inflicting direct damage -- there's no alternative. Later, of course, the magic-user will gain 3rd-level spells (if he or she lives!) and learn the staples of area damage, but not before learning to be clever about spell usage.
This is an interesting lesson for the burgeoning magic-user (and player!), because this teaches the use of spells to do things other than just hit enemies for damage. It's a way to think strategically about spell usage. This is important because many of the higher-level spells that the magic-user will gain depend on that kind of thinking. Fireball may always seem like an attractive spell, but it can only hit a specific area for a certain amount of damage, which enemies can mitigate via saving throw. Contrast with slow, which affects a larger area and can reduce enemy attack rate, thereby lowering their damage output, and offers no saving throw. Similarly, fly might seem to be a spell with only limited utility, until one remembers that even a lowly magic-user can be proficient with darts, with a throwing rate of 3 per round, and if the magic-user happens to have two 3rd-level spells, protection from normal missiles is also a possibility -- meaning that only enemy magic or extraordinary measures can strike the flying magic-user. Both spells have a duration over a turn, so they will last for at least 10 rounds of normal combat! This distinction becomes even greater at higher levels, when magic-users are considering the possible utility of spells like massmorph and glassee. By putting in a spell gap early on, the game forces players of magic-users to consider how they will structure their spell lists with utility in mind beyond just damage, and trains them to use those kinds of spells early in their characters' careers.
This training, of course, then carries on beyond just Dungeons & Dragons. Players who grew up with this gameplay learn to think about how to use their character abilities in ways beyond just "I hit the enemy for damage!". That kind of game strategy thinking is a process that they'll take with them to every other game they play.
Happy coincidence? Or mad genius?