dropping after it has reached the dew point thus, the condensation temperature measurement is lower than the actual dew point temperature before water starts to condense. Therefore, the temperature of the mirror is slowly increased until evaporation is observed to occur and the dew point is reported as the average of these two temperatures. By obtaining an accurate dew point temperature, one can calculate moisture content in the gas. The mirror temperature can be regulated by either the flow of a refrigerant over the mirror or by a thermoelectric cooler also known as a Peltier element. The formation behavior of condensation on the mirror's surface can be registered by either optical or visual means. In both cases, a light source is directed onto the mirror and changes in the reflection of this light due to the formation of condensation are detected by a sensor or the human eye, respectively. The exact point at which condensation begins to occur is not discernible to the unaided eye, so modern manually operated instruments use a microscope to enhance the accuracy of measurements taken using this method. Chilled mirror analyzers are subject to the confounding effects of some contaminants, however, at levels similar to other analyzers. With proper filtration and gas analysis preparation systems, other condensable liquids such as heavy hydrocarbons, alcohol, and glycol will not distort the results provided by these devices. It is also worth noting that in the case of natural gas, in which the aforementioned contaminants are an issue, on-line analyzers routinely measure the water dew point at line pressure, which reduces the likelihood that any heavy hydrocarbons, for example, will condense before water. On the other hand, chilled-mirror devices are not subject to drift, and are not influenced by fluctuations in gas composition or changes in moisture content. Chilled mirror combined with spectroscopy This method of analysis combines some of the benefits of a chilled-mirror measurement with spectroscopy. In this method, a transparent inert material is cooled as an infrared (IR) beam is directed through it at an angle to the exterior surface. When it encounters this surface, the IR beam is reflected back through the material. A gaseous media is passed across the surface of the material at the point corresponding to the location where the IR beam is reflected. When a condensate forms on the surface of the cooling material, an analysis of the reflected IR beam