Index indicates the degree, or power, to which a particle is raised. It consists of two letters, placed to the right of the symbol representing the particle. Thus, 'A.A.' signifies the 0th degree; 'B.A.' the 1st degree; and so on, till we reach 'M.A.' the 2nd degree (the intermediate letters indicating fractions of a degree); the last two usually employed being 'R.A.' (the reader need hardly be reminded of that beautiful line in The Princess 'Go dress yourself, Dinah, like a gorgeous R.A.') and 'S.A.' This last indicates the 360th degree, and denotes that the particle in question, (which is 1th part of the function 'Essays and Reviews,') has effected a complete revolution, and that the result = 0.
Moment is the product of the mass into the velocity. To discuss this subject fully, would lead us too far into the subject Vis Viva, and we must content ourselves with mentioning the fact that no moment is ever really lost, by fully