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Early-type galaxies are filled with hot X-ray emitting gas, but the study of the less plentiful cold gaseous component has been more challenging. Studies of cold material through IRAS 60µm and 100µm observations indicated that half of ordinary E and E/S0 galaxies were detected above the 3 level, indicating that cold gas is common, although no correlation was found between the optical and far-infrared fluxes. Most detections were near the instrumental threshold, and given an improved understanding of detection confidence, we reconsider the 60µm and 100µm detection rate. After excluding active galactic nuclei, peculiar systems, and background contamination, only 15 non-peculiar E and E/S0 galaxies from the RSA catalog are detected above the 98% confidence level, about 12% of the sample. An unusually high percentage of these 15 galaxies possess cold gas (HI, CO) and optical emission lines (H ), supporting the presence of gas cooler than 10 4 K. The 60µm to 100µm flux ratios imply a median dust temperature for the sample of 30 K, with a range of 23-38 K.These detections define the upper envelope of the optical to far-infrared relationship, F fir % F B 0.24±0.08 , showing that optically bright objects are also brighter in the infrared, although with considerable dispersion. A luminosity correlation is present with L fir % L B 1.65±0.28 , but the dust temperature is uncorrelated with luminosity. The dust masses inferred from the far-infrared measurements are an order of magnitude greater than those from extinction observations, except for the recent merger candidate NGC 4125, where they are equal. We suggest that the ratio of the far-infrared dust mass to the extinction dust mass may be an indicator of the time since the last spiral-spiral merger.These results are compared to the model in which most of the dust comes from stellar mass loss and the heating is primarily by stellar photons. Models that contain large dust grains composed of amorphous carbon plus silicates come close to reproducing the typical 60µm to 100µm flux ratios, the far-infrared luminosity, and the L fir -L B relationship.

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taken over ice cloud of visible optical thickness 0.1 and 0.3 are shown. These observations address the need for more measurements of radiance from cirrus, particularly in the far infrared, where experimental data are lacking. A test of consistency in modelling in both the far infrared and mid infrared is performed by fitting a model calculation of radiances in the infrared window region, and comparing with the measured radiances. In this consistency check, the sampling of the surrounding atmosphere and the cloud is given extensive consideration. The model was not able to consistently reproduce the observed radiance across the entire region, and was particularly poor in the 330-600cm −1 region of the far infrared. Possible causes are thought to be primarily model input uncertainties arising from inadequate sampling of cloud and atmosphere.