Sentence:  One may very easily fall into mistakes and errors when one is searching into the hidden causes of things, in the absence of real experiments, and this is easily apparent from the <WSD>crass</WSD> error of Cardan; who deems himself to have discovered the distances of the centres of the cosmos and of the earth through a variation of the magnetick iron of 9 degrees. 
Meaning of the word marked with <WSD> tags:  Lacking finesse; crude and obvious.