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A modified form of Boyle's Law is derived for a spherical mass of gas at Uniform temperature in equilibrium under its own gravitation and an external pressure, and a typical p–V curve is shown. Any such mass of gas is gravitationally unstable if sufficiently compressed. It is shown also that a sufficiently large isothermal gas sphere is unstable, and the condition for this is compared with Jeans' formula for gravitational instability. The relevance of the phenomenon to the formation of the nebulae is briefly considered.
W. B. Bonnar (Fri,) studied this question.