Splitting a class into multiple files in Ruby on Rails

I'm trying to split a large model into multiple files for logical organization. So i have two files:

model1.rb

class Model1 < ActiveRecord::Base
  before_destroy :destroying
  has_many :things, :dependent=>:destroy

  def method1
    ...
  end
  def method2
    ...
  end

end
require 'model1_section1'

model1_section1.rb

class Model1
  def method3
    ...
  end
  def self.class_method4
    ...
  end
end

but when the app loads, and there is a call to Model1.class_method4, i get:

undefined method `class_method4' for #<Class:0x92534d0>

i've also tried this for the require:

require File.join(File.dirname(__FILE__), 'model1_section1')

What am i doing wrong here?