摘要
來自天空的巨響，古人謂之「天鼓鳴」。這些巨響，包括可以理解的天氣雷暴以及一些莫名的「無雲而雷」聲響。有關惡劣天氣的雷暴現象，古今皆然，認識較多；至於其他與天氣無關的「天鼓鳴」，在通訊與科技不發達的古代，人們無法理解其真正發生原因，只得以「無雲而雷」如實記載下來。這些古代留下的奇特記錄，提供了我們可以重新探究自然界秘奧的線索。二十五史及各地方志的五行志中，有不少「天鼓鳴」及「無雲而雷」的記載。本文搜尋其他各種來自空中「如雷」的聲響，分析比對這些巨響發生的時空環境，參考現代地球科學經驜，它們大約可歸類為地震、山崩、山鳴、隕石墬地、潮水相擊、火山爆發等現象所引起的聲響。
並列摘要
From historical books and local chronological records, it is recognized that ancient Chinese is respectful to the destructive power of thunders. Occurrence of thunder usually signifies the coming of disaster that civilians and emperor will have to suffer in the near future, ”clear day thunders”, in particular, were often recorded in the past thousand years.To reveal the puzzle of ”clear day thunder” phenomenon, we search out all possible ”sky noises” and the related hazards from the records. After analogue reasoning, ”clear day thunders” may be attributed to earth quake, volcanic eruption, land slide, meteor strike, tidal wave, and etc.