The sentences I don't understand grammatically.

[yoojin]

Hi all.
Reading Mary Shelley's Frankenstein, I found the sentences whose structures I don't understand exactly.
Look at these sentences:

They[the blank and dreary northern shores of the Tay] were the eyry of freedom, and the pleasant region where unheeded I could commune with the creatures of my fancy.

I felt that blank incapability of invention which is the greatest misery of authorship, when dull Nothing replies to our anxious invocations.

First, I found the adjective "unheeded" between "where" and "I could [...] my fancy." an intruder. It seems to me that it's where it shouldn't be. I roughly know what the sentence means but not the adjective's role. Was it used as participle phrase? I'd like someone to paraphrase the sentence or to explain its exact grammatical... function or something.
Secondly, the sentence in which Shelley expressed the agony of invention. My friend said the word "dull" modified "Nothing" but if so, the meaning of the sentence will be... rather odd, won't it? In addition, "dull" should be after "Nothing", right? Was "dull" also used as participle phrase as "unheeded" above was? And one more, why does "Nothing" begin with a capital, in the middle?

[Soup]

Hello Yoojin,

The word unheeded is an adverb meaning without being noticed, disturbed, observed. It can go at the beginning of the sentence; it can go after the verb or it can go at the end of the sentence:

...the pleasant region where unheeded (adverb) I could commune with the creatures of my fancy.

• 
  
  • ...where I could commune unheeded with the creatures of my fancy.
  • ...where I could commune with creatures of my fancy unheeded.
  
  

__________________________

I felt that blank incapability of invention which is the greatest misery of authorship, when dull (adjective) Nothing (Subject) replies to our anxious invocations.

The word dull is an adjective. It modifies the subject Nothing, a personified noun. (See Personified | Define Personified at Dictionary.com)