為甚麼這裡沒有介詞連接？

The weather that day was really perfect.

"that day" functions as an adverb like today, tomorrow and yesterday, telling the time of event.

The adverb of time can also placed at the beginning or at the end of the sentence.

e.g. The weather was really perfect that day.
That day, the weather was really perfect.

2012-11-05 09:14:20 補充：
"That day" can also be used as a noun.

e.g. That day was my birthday. (Of course, "that day" refers to a day you have already mentioned in the previous sentences.)

The weather of that day was really perfect. 這句的that day 是否名詞？

The weather that day was really perfect.= oral English has the same meaning as the following sentence

The weather was really perfect on that day = proper written English


2012-11-05 19:56:32 補充：
that day - tells us more when the weather was perfect & has function of adjective here

You'll notice that (on that day)=adj.phrase ;
describing weather=subject.of the sentence.
"was" =the verb.

2012-11-05 12:28:13 補充：
That day(adv),the weather was really perfect.

i think it is because 'that day' is used to describe the 'weather'

2012-11-04 19:03:21 補充：
http://www.npc.edu.hk/staff/~ngtungying/english_grammar/
then click 目錄 and click lesson 30, Noun clause

Hope that i can help u :]