The summer night air was feverish. the whisper of the breeze curled within my ear. the crowd's roar was thunder. question how does the author use metaphors in the sentences

The writer uses metaphors in the sentences to exaggerate as it shows how loud the crowd was at night as they refer the noise of the crowd like thunder. Thuder is extremly loud. the writer describes the night air as feverish which tells the reader that it was a very cold night and someone could get a fever.

Explanation:

21 balloons is the story of professor william sherman's travels.

in 1883, he set off from san francisco for a balloon ride over the pacific and was found a month later floating with 21 balloons in the atlantic ocean. this seemed an astounding feat and everyone wanted to know what had happened.    

professor sherman was loyal, however, and said he would tell his tale first to the western american explorers club in san francisco, of which he was a member. this built up suspense for several chapters before he began to tell of the wonders of his adventures and the amazing island of krakatoa, an island which had just been blown up by a volcano.  

the residents of krakatoa are all millionaires who live under a "gourmet government" of their own devising. we get to see all the incredible adventures that creative people with unlimited resources would create according to the author.

sentence lenght varies according to word choice.you select which word to use and that will require to use other expressions that collocate with the word chosen.sentence length will vary   according to the choice of words you make to express your ideas.