[ATM] water interference

[shyam rathod <iloveyawli@yahoo.com>]

Dear list members  today was the first time i saw images of interference bands produed by flim of water and glass surface immerced in water many here might be familer with the test it is generally called water test or Rayleigh water test for an optical flat.
   
  inteference is an everyday phenomenon in nature u could see bands on rainy days when some oil or petrol from an vehical drops on water.
   
  I took a cell which i had made for my 8" and put it on base inverted then took a pan some inch bigger then my 4" flat to reduce capillary action and placed the 4"flat in the pan centered ,poured water till it was 1/16th of an inch (this cannot be measured but filled the water till a small flim of aqua is developed on the glass surface)then adjusted the screws of the cell i saw two images of the bulb then I co-inside this two images when i saw a single image it indicated the water flim and the glass surface were parallel ,and magically it happend I saw interference bands but the bulb images here should coincide accrately and this adjustment should be very fine,to get bands.
  u can cover the pan with glass to exclude water from having micro ripples from air current i did not cover the pan as i did not have problem of air current or vibrations as i was alone in a location. 
  as the water evaporates the  gap bettween glass and water flim reduces and u can judge if it is concave or convex as said by Mr.Parker in his artical in amature telescope making journal on flat testing.
  this test is very usefull for making optical flats of 8" size as the water surface is lamda /675 approx wave correct for an 8" flim.
  mention in one of the book of ingalls to test 200" flat with this test however introdues a error of 2 wave as earth gravitational field is a spherical and the flim has some convexity.
  though i think to make big flats in future one need a flat vector gravitational field .
  other applications: this test is very sensitive to vibrations with slightest disturbance the bands disturb i think we could use it in determining sesmic activities and detecting slightest vibrations.
  disadvantage: the band are of low contrast
  thanking to all the list members 
  shyam rathod
  INDIA
   
   

 		
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