Final answer:
The dominant feeling on the Saturday in question was lethargy, due to the reference to a 'day of lassitude'.
Step-by-step explanation:
The dominant feeling experienced on that Saturday was one of suspense and unease, as the day was described with words such as 'suspense', 'lassitude', 'fluctuating barometer', 'slept but little', and 'rose early', which indicate an underlying tension and discomfort. Of the options provided, the dominant feeling aligns most closely with lethargy due to the mention of 'lassitude', a state of physical or mental weariness; however, the overarching mood seems to be one of anxious anticipation or apprehension, given the context of suspense. Therefore, fear or suspense would also be appropriate descriptors of the dominant feeling, though these are not provided as options in the question.