Here's the first passage:
"Far through unfrequented woods on the confines of towns, where once only the hunter penetrated by day, in the darkest night dart these bright saloons without the knowledge of their inhabitants….They go and come with such regularity and precision, and their whistle can be heard so far, that the farmers set their clocks by them, and thus one well-conducted institution regulates a whole country. Have not men improved somewhat in punctuality since the railroad was invented? Do they not talk and think faster in the depot than they did in the stage-office? There is something electrifying in the former place."The Fitchburg Railroad had been very recently built in his time. Despite the short time it had been in existence, already it had begun to change the way people who lived near it regarded time.
It may sound like Thoreau admires this change, but he does not. Just a little earlier he wrote that when he was at Walden his "days were not days of the week, bearing the stamp of any heathen deity, nor were they minced into hours and fretted by the ticking of a clock." His Walden-time is not "minced into hours." That is, it is not governed by any clock but Thoreau himself.
The other passage is one where he imagines the trains as "bolts" or arrows:
"We live the steadier for it. We are all educated thus to be sons of Tell. The air is full of invisible bolts."To be a son of William Tell is no pleasant thing. To be a son of Tell is to be constantly in mortal peril. One's schoolmaster is the permanent risk of sudden death.
A hundred and seventy years ago Thoreau was already seeing the ways that a single technology - one heralded as beneficent and neutral - was remaking us in its image, changing our sense of time, speeding us up, educating us to stay out of its way and so confining us to the spaces between the spaces it occupies.
And it's not just those who ride the railroad who are conditioned by it; everyone is conditioned by it. The technology is not neutral, not a mere thing we can wield with no effect upon the wielder. We may devise tools, but we are ignorant if we think that the tools do not also come to change us.