|— Hiccup explaing the magnifying glass to Fishlegs|
The Magnifying Glass is an invention seen and mentioned several times in the How to Train Your Dragon Franchise. It is implied that Hiccup created it in the Season 3 episode, "Buffalord Soldier", but is seen in use in earlier episodes.
In the episode "Reign of Fireworms", the Twins find a stone on Dragon's Edge with worn writing on it. They dub it the Namey Rock, and say it was left by an ancestor claiming the island. This means that the Twins own Dragon's Edge. Gobber travels to Dragon's Edge to verify the script and uses a magnifying glass to closely inspect it.
In "Buffalord Soldier", Hiccup and the Dragon Riders arrived on Odin's Respite in an attempt to find a Buffalord in order to gather its saliva to cure Astrid of the Scourge of Odin. While on the island, the Riders attempted to find the dragon by following its tracks, but when they abruptly ended, Hiccup attempted to use the magnifying glass to see if he could find any other trace of the dragon. He implies that he recently invented it. Eventually, he was able to find a dragon scale, showing that the Buffalord was nearby and spurring the Riders to keep searching.
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The magnifying glasses appearing in the Franchise take two different forms. The one used by Gobber is designed like the Spyglass, where the user holds a short tapering tube, looks through the narrow end to the wider end that has a convex lens.
Hiccup uses a magnifying glass with a large convex lens held with a thin wrap around frame and a handle at the bottom.
The magnifying glass was created by Hiccup so that he could view small objects up close. This enables him or any other users to observe the object in question in greater detail.