1.3384 (!) (h86-A-T40,0124.58) (107?) 
refractive index of sea water 
wavelength of light in nanometers 
temperature in degrees Celsius 
water depth in feet 
salinity in parts per thousand. 
For the special case of distilled water, the salinity is equal 
to zero parts per thousand. Assuming a water depth of zero, 
Eq. 1 reduces to the following simplified form for distilled 
water at atmospheric pressure: 
nz 1.3384 (4) (486-A-2) (1075) Eq. 2 
n nu n ow dH 
During my April 1975 visit to E. Leitz Canada Limited that 
you initiated, Walter Mandler mentioned that a new ELCAN water 
contact lens was being designed and manufactured for Westing- 
house. I requested Mandler to advise me as to the water re- 
fractive index equation that was used for the lens design. 
Mandler left the conference room and soon returned to advise 
that Westinghouse correspondence referred to Eq. 10-1 of Ref. 1. 
Since last April, I have been interested in determining if the 
degree of accuracy of Eq. 10-1 is acceptable for present day 
use within a more sophisticated underwater optical industry. 
Linear Eq. 10-1 was derived in 1968 as an initial presentation 
which is subject to refinement as the state-of-the-art advances. 
An equation to determine the refractive index of distilled 
water with greater accuracy than Eq. 2 is derived by means of 
the Cauchy Equation which is presented as follows: 
n nb aci Eq. 3 
where 
distilled water refractive index 
constant 
constant 
constant 
wavelength of light in nanometers. 
n nud 
The three wavelengths representing the spectrum of interest 
in the underwater environment are: 
= 4 50nm 
= 500nm 
= 550nm. 
The three indexes of refraction for distilled water at 0°C 
that correspond to the above-listed wavelengths are extracted 
from Table 7 of Ref. 2 and are presented as follows: 
= 1.302362 
1.3374146 
zm 143352917.