为啥明清时代军人都喜欢在头盔上插根“避雷针”？

为啥明清时代军人都喜欢在头盔上插根“避雷针”？
If this picture is your intelectual property (copyright infringement) or child pornography / immature images, please Contact Us for abuse. We will follow up your report/abuse within 24 hours.

Image Source : k.sinaimg.cn