How Is the Red Part of Stratton's Equation Derived from Light Pressure?

[mertcan]

Hi everyone, initially I would like to put into words that this equation in my attachment is provided by Julius Adams Stratton but he do not derive the equation. The only part I do not understand and can not derive is the "RED" part. He just says it results from light pressure. So, I would like to ask : How can we reach this formula painted with RED? How do we derive this part ?

 

[DrClaude]

What is reference 19?

 

[mertcan]

What is reference 19?

 

[mertcan]

What is reference 19?

Additionally, I have the book but nothing is derived...So, Any idea related to how to derive the "RED" part?

 

[mertcan]

@DrClaude Could you express something about my question after I shared the reference?

 

[DrClaude]

@DrClaude Could you express something about my question after I shared the reference?

I dinät have access to that book right now, so I can't help for the moment. Maybe someone else will chime in in the mean time.