Basic postulates of some coordinate transformations within material media

Abstract: The paper aims to explore the physical quantities of several invariants, including the basic postulates of some types of crucial coordinate transformations, conservation laws and continuity equations, in the electromagnetic and gravitational fields. J. C. Maxwell first utilized the quaternions to describe the electromagnetic theory. Subsequent scholars make use of the octonions to study the physical properties of electromagnetic and gravitational fields simultaneously, including the octonion field strength, field source, angular momentum, torque and force. When an octonion coordinate system transforms rotationally, the scalar part of one octonion will remain unchanged, although the vector part of the octonion may alter. In the octonion space $\mathbb{O}$ , some invariants can be derived from this octonion property. A part of these invariants can be selected as the basic postulates of Galilean transformation or Lorentz transformation. Similarly, it is able to derive several invariants from the octonion property, in the transformed octonion space $\mathbb{O}_u$ . And that the invariants can be chosen as the basic postulates of a few new types of coordinate transformations. Further, the combination of invariants in the octonion spaces can be applied as the basic postulates of some new coordinate transformations, relevant to the norm of physical quantities. Through the analysis, it is easy to find that each conserved quantity has its preconditions from the perspective of octonion spaces. This is helpful to deepen the further understanding of the physical properties of conservation laws and other invariants.