VII. On the transfinite cardinal numbers of well-ordered aggregates
Philip E. B. Jourdain · The London Edinburgh and Dublin Philosophical Magazine and Journal of Science · 1904
~-t%'an,~nite Cardinal zVambers of Well-ordered Aggregates.61 average range of vertical disturbance being about "00140 C.G.S., differences of this order may be obtained by supposing that the slabs of magnetic matter are 16 kiloms.(10 miles) thick, and that the upper surfaces are 4 kiloms, from the surface of the earth.We may, however, arrive at a similar result by assuming that iron exists iu the crust of the earth chiefly in the form of magnetite and iron ores, and that the temperature at which these cease to be magnetic is 555 ~ C. With a rise of temperature of 1 ~ per 90 feet of depth this would give adepth of 15 kiloms, or 9~ miles, as the thickness of the magnetic floor, a value which corresponds with that calculated from a knowledge of the range of vertical disturbance.In concluding this description of the experiments, which were carried out in the Physical Laboratory of Birmingham University, I take the opportunity of expressing my thanks to Prof. Poynting for suggesting the investigation, providing the necessary apparatus and space, and for much encouragement and assistance during the progress of the experiments.I am also indebted to all the members of the Geological Department of the same University for their cordial assistance with the geological side of the investigation.