地球磁鞘之電漿具有溫度非均向性之特性，為測試壓力非均向磁流體理論之最佳電漿實驗室。本論文將分析AMPTE/IRM人造衛星穿越地球磁鞘所收集之電子與質子密度、溫度與磁場資料，探討其熱力狀態。我們檢驗不同之能量方程，包括廣義Chew-Goldberger-Low （CGL） laws或雙絕熱定律、double-polytropic laws與修正之雙絕熱定律。其中，double-polytropic laws含有兩個自由指數，可描述絕熱與等溫等之各種熱力狀態。分析結果顯示，磁鞘之質子與電子均嚴重違反CGL或雙絕熱定律，一般較接近等溫狀態。而由測試修正之雙絕熱定律可探討電漿之非完全導體與熱通量效應。 The magnetosheath is considered to be an ideal plasma laboratory for testing the anisotropic MHD theory. In this thesis, we examine the thermodynamic properties of the magnetosheath protons and electrons by analyzing the plasma and magnetic field data from the AMPTE/IRM satellite. We check various energy equations including Chew-Goldberger-Low (CGL) or double-adiabatic laws, double-polytropic laws and modified double-adiabatic laws. The double-polytropic laws proposed by Hau et al. (1993) as an energy closure to the MHD equations contain two polytropic exponents and thus can describe different thermodynamic properties, such as the double-adiabatic and double-isothermal cases. The analysis results for both protons and electrons show that the double-adiabatic laws are severely violated in the magnetosheath and the double-polytropic laws with suitable exponents may serve as a viable energy closure. In most cases the plasma is close to the isothermal state. The relative importance of non-perfect conducting and heat flux effects may be inferred from the test results of modified CGL laws in the magnetosheath.