sentences:  He quickly concluded that the short term variations were due to the day/night cycle, while the longer term ones were due to the number of visible sunspots.He published two introductory papers on the topic in the "Philosophical Transactions of the Royal Society".The first, in 1851, was a collection of early measurements; the second in 1852 correlated with Heinrich Schwabe's sunspot measurements, which had been made widely available in Alexander von Humboldt's "Cosmos", also published in 1851.