Sentence:  It was very different, when the masters of the science sought immortality and power; such views, although futile, were grand: but now the scene was changed. The ambition of the inquirer seemed to limit itself to the annihilation of those visions on which my interest in science was chiefly founded. I was required to exchange <WSD>chimeras</WSD> of boundless grandeur for realities of little worth. 
Meaning of the word marked with <WSD> tags:  A foolish, incongruous, or vain thought or product of the imagination.