This works:
\documentclass[oneside,english]{book}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{geometry}
\geometry{verbose,letterpaper,tmargin=1in,bmargin=1in,lmargin=1.25in,rmargin=1.25in}
\setcounter{secnumdepth}{3}
\setcounter{tocdepth}{3}
\setlength{\parskip}{\medskipamount}
\setlength{\parindent}{0pt}
\usepackage{setspace}
\doublespacing
\let\oldchap=\chapter
\renewcommand*{\chapter}{%
\secdef{\Chap}{\ChapS}% whether there's a star or not...
}
\newcommand\ChapS[1]{\singlespacing\oldchap*{#1}\doublespacing}
%The first argument to \chapter is optional, hence the need for "[]"
%in the following definition. However, \secdef duplicates the mandatory
%argument if no optional argument was given. So we'll always have that
%argument and the default doesn't matter.
\newcommand\Chap[2][]{\singlespacing\oldchap[#1]{#2}\doublespacing}
\makeatletter
\usepackage{babel}
\makeatother
\begin{document}
\tableofcontents{}
\chapter{The First Chapter}
Here is some stuff. Here is some stuff.Here is some stuff.Here is some
stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here is
some stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here
is some stuff.Here is some stuff.Here is some stuff.Here is some
stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here is
some stuff.Here is some stuff.Here is some stuff.
\chapter{The Second Chapter Has a Very, Very, Very Long Title}
More stuff. Here is some stuff.Here is some stuff.Here is some
stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here is
some stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here
is some stuff.Here is some stuff.Here is some stuff.Here is some
stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here is
some stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here
is some stuff.Here is some stuff.Here is some stuff.Here is some stuff.
\chapter*{A Chapter with No Number}
What a bummer that is.Here is some stuff.Here is some stuff.Here is some
stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here is
some stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here
is some stuff.Here is some stuff.Here is some stuff.Here is some
stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here is
some stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here
is some stuff.Here is some stuff.Here is some stuff.Here is some
stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here is
some stuff.Here is some stuff.Here is some stuff.Here is some stuff.
\chapter[Not So Long in the Toc]{And Yet Another Very, Very, Very Long
Title}
More stuff. Here is some stuff.Here is some stuff.Here is some
stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here is
some stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here
is some stuff.Here is some stuff.Here is some stuff.Here is some
stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here is
some stuff.Here is some stuff.Here is some stuff.Here is some stuff.Here
is some stuff.Here is some stuff.Here is some stuff.Here is some stuff.
\end{document}
--
==================================================================
Richard G Heck, Jr
Professor of Philosophy
Brown University
http://bobjweil.com/heck/
==================================================================
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