The history of ultra-high energy cosmic ray physics is reviewed from the post-war era of arrays such as Volcano Ranch. Haverah Park and Akeno to the development of air-fluorescence and current hybrid arrays. The aim of this paper is to present the background information needed for a better understanding of the current issues in this field that are discussed in much greater depth in th... https://www.jmannino.com/quick-offer-Viqua-F4-50-Plus-Monitored-UV-System-Powered-by-UVMax-15-gpm-230-Volt-on-sale/