 Using the measurements from the Toronto and Hobart sites , Sabine noticed both short @-@ term fluctuations in magnetic declination over a period of hours , and longer @-@ term variations over months . 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 <unk> . 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 <unk> 's sunspot measurements , which had been made widely available in Alexander von Humboldt 's Cosmos , also published in 1851 . With further data collected from the Toronto site , Sabine was able to demonstrate conclusively that the eleven @-@ year sunspot cycle caused a similarly periodic variation in the Earth 's magnetic field . He presented a third and conclusive paper on the topic in 1856 , " On <unk> Laws <unk> in the Mean Effects of the Larger Magnetic <unk> " , in which he singled out the Toronto site for particular praise . 
