Say you live in an age of balloons and explosives. Perhaps, you think, it is time to start putting those two things together.
Today global humanitarian efforts continue to deal with the land mines leftover from past wars. At one point in history, it looked like they were going to have to deal with air mines as well. During the 1910s, when people saw the world getting more dangerous, it occurred to them that the new flying machines might be used for war. It also occurred to them that there were few options for anyone who wanted to protect themselves against the flying machines.
They decided the best way to protect themselves was to put mines in the air. The idea isn't entirely impractical. During World War II, Japan sent balloons with bombs attached to them wafting across the Pacific Ocean - but they were bombs, not mines. World War II also had "barrage balloons." For the most part, they were placed in areas in which enemy aircraft might swoop down and fly low. The balloons, shaped like blimps and anchored with heavy cables, were meant to catch planes with their cords, or just make the approach more difficult. Some even had small explosives that would cause damage to a plane, but not blow up a whole section of ground if the balloon fell down.
In 1916, on the other hand, people wanted hair trigger bombs that would blow up anything nearby. The idea was to hang them on balloons. The bomb's weight alone wouldn't pull the trigger down, but the slightest breeze from a passing aircraft would. These balloons would be sent up into the clouds, where airplanes couldn't spot them. Also, presumably, where they'd do little damage when they exploded due two light winds and passing geese. In the end, airplane and missile technology moved so fast that these would probably never have been of practical use. If they had been floated - imagine the carnage as they eventually dropped out of the sky and countries bombed themselves. Or imagine the world we would live in if the bombs somehow stayed afloat and we'd all have to stick to trains.