It has been well observed of Ferdinand and Isabella, that they lived together, not like man and wife, whose estates are in common, under the orders of the husband, but like two monarchs, strictly allied.

句子摘自《美国语文》中学课文 第5课 Ferdinand And Isabella 费迪南德与伊莎贝拉 

作者：Washington Irving

背景知识：FERDINAND AND ISABELLA were the King and Queen of Spain who supplied Columbus with ships and men to prosecute his voyage of discovery.

请教各位老师,

1)    observe of 是什么用法？字典上为何查不到此固定搭配？是否还可以这样说It has been well observed about… … 或It has been well observed that … … ？

2)    时态问题: 句中has been observed of … 指的是已经被观察了（现在之前发生过的一次），还是一直被观察（一直持续到现在的状态）？Observe不是短暂动作动词，对吗？所以，这里的现在完成时态“has been observed of … … ”该如何理解呢？谢谢老师。