The first asteroid, Ceres, was discovered in 1801, although it wasn't called an asteroid yet. Pallas, Juno and Vesta were discovered shortly after. Then no new asteroids were discovered for 38 years, until Astraea in 1845 when the rate of discovery picked up again, with the 10th asteroid (Hygiea) discovered in 1849.
Why was there such a decrease in new discoveries after the first four asteroids were discovered? And why did it pick up again a few decades later?
Was there a technological advance in the 1840s that made it possible to observe asteroids that were un-observable in the 1810s? Was the drop due to a decrease of interest in the astronomical community for objects between Mars and Jupiter? Did astronomers think they had found them all and stopped searching?