Equation (Chandrasekhar, Newton's Principia)

[Poetria]

Homework Statement

I am reading a book by Chandrasekhar, "Newton's Principia for a Common Reader." I don't understand some notation.

Homework Equations

(2) A(1)S(1) x A(1)D(1)=(A(1)B(1))^2

What does x means here? A cross product? Could you give me a hint where to find a good introduction to these geometrical operations? Obviously, there is a gap in my background.

 

[Ray Vickson]

Homework Statement

I am reading a book by Chandrasekhar, "Newton's Principia for a Common Reader." I don't understand some notation.

Homework Equations

(2) A(1)S(1) x A(1)D(1)=(A(1)B(1))^2

What does x means here? A cross product? Could you give me a hint where to find a good introduction to these geometrical operations? Obviously, there is a gap in my background.

It looks like a simple "times" = "multiplication" sign.

 

[Poetria]

It looks like a simple "times" = "multiplication" sign.

Oh, ok. I am overegging the pudding then. :) Many thanks. :) Sometimes he doesn't use it you know.

 

[Ray Vickson]

Oh, ok. I am overegging the pudding then. :) Many thanks. :) Sometimes he doesn't use it you know.

Just for future reference: the × sign could not be a cross-product, because that would give you an equation with a vector on one side and a scalar on the other. Besides, Newton wrote Principia hundreds of years before the invention of vectors and cross-products, etc (although, of course, maybe Chandraskhar is using modern notation and concepts in writing about Newton's work).

 

[Poetria]

Just for future reference: the × sign could not be a cross-product, because that would give you an equation with a vector on one side and a scalar on the other. Besides, Newton wrote Principia hundreds of years before the invention of vectors and cross-products, etc (although, of course, maybe Chandraskhar is using modern notation and concepts in writing about Newton's work).

Indeed he does use modern notation. And in the precedent chapter he employs the same sign with vectors. In addition, he refers to the concept of versed sine, which is little used but fortunately I have found a good definition.
I have also found "A History of Vector Analysis." :)
Thank you very much. It is tough stuff. :)