'Well into' and 'By'
Hello,

Here are two sentences I'm stuck.

I'd like to know each specific period from two sentences.

1. Well into the nineteenth century.…
does 'well into' mean some period from 1830 - 1850 or so?

2. By 1900, …
does 'by 1900' mean around 1890~1905 or so?

Question

'Well into' and 'By'
Hello,

Here are two sentences I'm stuck.

I'd like to know each specific period from two sentences.

1. Well into the nineteenth century.… 
does 'well into' mean some period from 1830 - 1850 or so?

2. By 1900, …
does 'by 1900' mean around 1890~1905 or so?

Answer

1.  Yes.
I'd say that that's exactly the period we're talking about. Not the beginning of the century, but a few decades in.

2.  No. 
It refers to the period which ENDS in 1900.  
If you say that something had disappeared by 1900, it means that the disappearance was going on during the 1890s.  By the time 1900 came around, the disappearance was complete.

Answer

Yes Correct for both sentences. But first sentences is a little bit out.
Different people would interpret the times a little differently.

First sentence after 1850 and closer to 1875-1885
Second sentence after 1850 :: -> 1890-1899 or a slightly earlier start date, but before 1900 end date.