'Midnight Rising'.

To the Editor: While I very much enjoyed Kevin Boyle's review of Tony Horwitz's ''Midnight Rising: John Brown and the Raid That Sparked the Civil War'' (Oct. 30), I found the following comment curious: ''It's impossible to read this fine book without thinking about the modern-day Browns, soldiers of a vengeful God, seeking righteousness in a fierce burst of violence, justice in the shedding of blood. Maybe Horwitz decided that he didn't need to make the comparison explicit.'' [ABSTRACT FROM AUTHOR]