We report on observations of interstellar dust emission at |b| <= 3.5 deg and l ~ 46(deg) with the Far Infrared Photometer (FIRP) on board the Infrared Telescope in Space (IRTS). The FIRP is a four-channel photometer with bands centered at 150, 250, 400, and 700 mu m and with a spatial resolution of 0.5 deg (FWHM). The 150--250 mu m and the 250--400 mu m brightness ratios of the interstellar dust emission show a slight decrease with increasing galactic latitude at |b| <= 3.5 deg, consistent with the 140--240 mu m brightness ratio observed by COBE/DIRBE. The 250--700 mu m brightness ratio shows a much stronger dependence on the galactic latitude. The effect may be due to a single component of warm (T ~ 20 K) dust with an emissivity index of n < 2, that decreases with galactic latitude. Alternatively, the effect may be due to the existence of two components of dust, a warm (T ~ 20 K) component and a cold (T ~ 4--7 K) component, each with an emissivity index of n = 2. In the latter case, either the temperature or the optical depth of the cold component increases as a function of the galactic latitude. In either case, the physical properties of the interstellar dust must be assumed to vary significantly over the range |b| <= 3.5 deg.