the meaning of "spectroscopic gayety"
What is the meaning of "spectroscopic gayety" in the following passage?
Why does it have to be guarded against?

[
Instead of rambling, this party had preserved a dignified homogeneity, and assumed to itself the function of representing the staid nobility of the country-side — East Egg condescending to West Egg, and carefully on guard against its spectroscopic gayety.
]

Ch.3
http://ebooks.adelaide.edu.au/f/fitzgerald/f_scott/gatsby/complete.html#chapter3

Question

the meaning of "spectroscopic gayety"
What is the meaning of "spectroscopic gayety" in the following passage?
Why does it have to be guarded against?

[
Instead of rambling, this party had preserved a dignified homogeneity, and assumed to itself the function of representing the staid nobility of the country-side — East Egg condescending to West Egg, and carefully on guard against its spectroscopic gayety.
]

Ch.3 
http://ebooks.adelaide.edu.au/f/fitzgerald/f_scott/gatsby/complete.html#chapter3

Answer

East Egg represented old money - people that had inherited it.  West Egg refers to new money - people that had recently gotten wealthy.  People from old money looked down on people with new money.  "Spectroscopic gayety" refers to loud or boisterous celebration - some observable sign that you came from new money.  "Spectroscopic" I think refers to 'observable', something you could analyze - in this case analyze a person's class.