Conversion to Lat/Lon from EPSG:54004?

[Kirk Holbrook]

Hi,

Does anyone have Javascript code to convert to Lat/Lon from EPSG:54004?

I found the following, but I'm not sure if it's correct. Also, I assume 
that I'd use two different radii for the R values below: for x, R = 
6378137.0 m; for y, R = 6356752.3142 m.

x = R(lon_rad)
y = R ln [tan((pi/4)+lat_rad/2)]

where R=radius of a sphere in map units, lon_rad=longitude in radians
(rad=deg/57.2957795), lat_rad=latitude in radians,  pi=3.14159..., 
ln=natural
log, x and y in meters.

If this is correct, then:

lon_degrees = x_meters / 6378137.0 * 57.2957795
lat_degrees = ??? [sorry my math skills are a bit out of date]

Any help is greatly appreciated!

Thanks,
Kirk