detector 26 can be either a photographic or electronic detection system at the user 39 s option detector 26 can include means for comparing observed spectral with known patterns fig3 5 and 6 show alternative embodiments of the present invention fig3 shows use of a folding mirror 40 folding mirror 40 permits other elements to be located outside of the cavity of the spiralling toroidal mirror 16 fig4 uses two spiralling toridal mirrors 16 rotating counter to one another this arrangement permits increased spectral range since both components have varying pathlengths from the beamsplitter fig5 uses a convex spiralling toroidal mirror 16 the convex reflecting surface is the exterior surface this arrangement permits several units to be placed around the convex mirror fig6 has a canted spiralling toroidal mirror 16 the principle ray of the incoming radiation 10 is at an angle of 45 u00b0 with the rotational axis of the mirror this permits the space in front of the mirror to be completely open providing easy access for cutting tools an optical frame 40 is supported by an air bearing 42 they support an optical cylinder 44 which is adjusted by aligning and clamping screws 46 fig6 also shows means for comparing known spectra with observed.