What's this optical dispersing prism called?

There is a multiple-element prism used in optics just for dispersing light by color, while allowing the light to pass straight through (for some middle wavelength like 515 nm). It is long and of rectangular or square cross section, and has entry and exit faces at the ends. The light travels along the long axis. There are alternating wedges of glass cemented together, the wedges having similar indices of refraction but very different indices of dispersion. Since indices of dispersion don’t really vary all that much in absolute terms, this prism gives a fairly small dispersion for such a large and expensive piece of glass, but it has its uses. I know that it is used in some handheld spectroscopes, and I saw them advertised in a catalog once, and have certainly seen diagrams of them, but can’t find any of that now. I thought it was called a “Nicole prism”, but that is just one of several similar-looking polarizing prisms. Though it only has two elements, a Nicole prism does look like a short and simple version of the thing I’m talking about.

Anybody know???

A Double Amici prism?

Wow, Fear, thanks - I think you’ve got it!

Actually, it’s more commonly called a Direct Vision Prism. That’s what we generally called them, and it’s how it’s entered in The Penguin Dictionary of Physics. The name Double Amici Prism can be confusing a.) because Amici prisms are often used to re-direct light by 90 degrees, often interchanging right and left as well (as in Smith’s Modermn optical Engineering and b.) Some Direct-Vision Spectroscopes use more than three elements. The one sold by Edmund Optical has five:


Here’s one that covers all bases – an Amici Direct Vision Prism:


I’ve had the Edmund device for years. It’s very handy.

Can’t find my Penguin dictionary, and neither term is in the index of my Handbook of Optics. The spectroscopy chapter is only about the data, not the equipment.