50 Years Ago
With the growth of telecommunications based on geostationary orbits, there is growing concern that satellites may become so closely crowded together that they interfere with each other … An article in the current issue of the Proceedings of the Institution of Electrical Engineers … consists of a calculation of the capacity of the equatorial orbit to accumulate geostationary communications satellites. Their chief conclusion is that the capacity of the equatorial orbit, with present arrangements, is probably limited to about 2,000 telephone circuits for each degree of the orbit. For practical purposes, this amounts to roughly one satellite in each four degrees of the orbit, which in turn implies that it may take very little further development before parts of the equatorial orbit — over the Atlantic and America, for example — may be overcrowded.
100 Years Ago
The war has been responsible for great developments in many branches of science … [C]lose attention has been given to the subject of marine physics … especially … submarine acoustics … The singular property which distinguishes a submarine from other ships is its capacity of rendering itself invisible when pursued or when seeking and attacking its prey. Robbed of this power, it is an extremely vulnerable craft … The acoustic method of detecting a submerged submarine … was found to be far more sensitive and to give a much longer range than all other methods. Instruments used for this purpose are called hydrophones. … [T]he improved hydrophones developed for war service should greatly reduce the dangers of collisions and shipwreck.
Nature 572, 320 (2019)