The present invention relates to a method and apparatus for measuring the relative humidity in a solid state, micro-environmental system, and more particularly to such a system wherein an adsorbent, having a characteristic dewpoint and a temperature hysteresis, is used for drying an exhaust air flow. The relative humidity of a gaseous material is defined as the ratio of the partial pressure of the water vapor to the vapor pressure of pure water at the same temperature. The quantity of water vapor in the air will be the same as the water vapor that would be present if the relative humidity were 100 percent, i.e., at saturation. Thus, to remove moisture from air, it is necessary to remove the equilibrium vapor from air having a relative humidity less than 100 percent. That is, a gas must be dried at a relative humidity less than 100 percent in order to remove water vapor. A common humidity sensing device to measure the relative humidity in the air is the hygrometer. A hygrometer is an instrument that measures the relative humidity of air. Typical examples of hygrometers are those based upon the capacitance principle or the thermocouple principle. Thermisters are often used in the former devices. An inherent disadvantage of hygrometers is that their response time is too slow for many applications and requires large and expensive components. In addition, hygrometers are sensitive to changes in air velocity and the temperature range over which they operate. This lack of sensitivity makes their use at very low or very high temperatures difficult or impossible. Therefore, a need exists for an improved method and apparatus for measuring the relative humidity of a gas. The present invention addresses this need. A method and apparatus for measuring the relative humidity of a gas according to the invention measures the relative humidity of a gas by passing the gas through an adsorbent. The adsorbent has a characteristic dewpoint that changes as the adsorbent dries. Therefore, the adsorbent operates in an equilibrium state, even when the system in which the adsorbent is disposed changes between dry and humid conditions. This change in the equilibrium state of the adsorbent results in a change in the electrical conductivity of the adsorbent. This change can be detected to measure the relative humidity of the gas in which the adsorbent is disposed. In one aspect, the invention is directed to a method for measuring the relative humidity of a gas, comprising providing a gas that is to be measured for relative humidity and providing an adsorbent having a characteristic dewpoint that changes as the adsorbent dries. The adsorbent is disposed within a micro-environmental system having at least one surface and comprising first and second electrodes that are spaced apart. The first electrode is in contact with the adsorbent and a change in the electrical conductivity of the adsorbent is measured. The relative humidity of the gas is determined based upon the change in the electrical conductivity of the adsorbent, whereby the relative humidity of the gas can be measured. In another aspect, the invention is directed to a method for measuring the relative humidity of a gas, comprising providing a gas that is to be measured for relative humidity, providing an adsorbent having a characteristic dewpoint that changes as the adsorbent dries and being disposed in a micro-environmental system having at least one surface. The micro-environmental system has a first portion and a second portion. The first portion is separated from the second portion by a barrier wall. The adsorbent is located in the first portion of the micro-environmental system. A first electrode is disposed in the first portion and a second electrode is disposed in the second portion. The first electrode is in contact with the adsorbent, and a change in the electrical conductivity of the adsorbent is measured. The relative humidity of the gas is determined based upon the change in the electrical conductivity of the adsorbent, whereby the relative humidity of the gas can be measured. In yet another aspect, the invention is directed to an apparatus for measuring the relative humidity of a gas, comprising a micro-environmental system having at least one surface and comprising a barrier wall separating first and second portions of the micro-environmental system. The apparatus further comprises an adsorbent that is disposed in the micro-environmental system. The adsorbent has a characteristic dewpoint that changes as the adsorbent dries. A first electrode is disposed in the first portion of the micro-environmental system and a second electrode is disposed in the second portion of the micro-environmental system. The second electrode is spaced apart from the first electrode by the barrier wall. The first electrode is in contact with the adsorbent and a change in the electrical conductivity of the adsorbent is measured. A control system coupled to the first electrode and a detector coupled to the second electrode controls a pressure in the micro-environmental system and the relative humidity of the gas is determined based upon the change in the electrical conductivity of the adsorbent, whereby the relative humidity of the gas can be measured. The present invention further provides a micro-environmental system for measuring the relative humidity of a gas. The micro-environmental system comprises a barrier wall separating first and second portions of the micro-environmental system. The system further comprises an adsorbent that has a characteristic dewpoint that changes as the adsorbent dries. A first electrode is disposed in the first portion of the micro-environmental system and a second electrode is disposed in the second portion of the micro-environmental system. The second electrode is spaced apart from the first electrode by the barrier wall. The first electrode is in contact with the adsorbent and a change in the electrical conductivity of the adsorbent is measured. A control system coupled to the first electrode and a detector coupled to the second electrode controls a pressure in the micro-environmental system and the relative humidity of the gas is determined based upon the change in the electrical conductivity of the adsorbent, whereby the relative humidity of the gas can be measured. Additional advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.