Like Feinberg and Sherman (1985) and Phillips and Mason (1992), we test experimentally whether conglomerate firms, i.e. firms competing on multiple, structurally unrelated markets, effectively limit competition. Unlike these authors, our more general analysis assumes differentiated rather than homogeneous products and distinguishes strategic substitutes as well as complements to test their forbearance hypothesis. We vary the duration of the interaction to disentangle effects of forbearance and repetition. Surprisingly, rather than limiting competition, conglomerate firms foster it. In line with our expectations, we find more cooperation with strategic complements than with strategic substitutes and also more cooperation with long term than with short term interaction.

The properties of a nonfocusing collimating parabolic telescope are studied in detail by a ray-tracing method. The best optical quality with respect to coma and astigmatism is calculated for rays close to the optical axis of the telescope. For rectangular fields of view the borders are not sharp because of the aberration. A combination of a parabolic telescope and an echelle-type spectrometer gives very high spectral resolution. Wadsworth, Ebert-Fastie, and other types of spectrometers are equally well suited to be combined with this telescope. For some cases spot diagrams demonstrate the optical performance. In addition, diffraction by the aperture and its implications are discussed.

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