This should prove helpful: 
 
@ARTICLE{machlup_penrose50jehist, 
  author = {Machlup, Fritz and Edith Penrose}, 
  year = 1950, 
  title = {The Patent Controversy in the Nineteenth Century}, 
  journal = {Journal of Economic History}, 
  volume = 10, 
  number = 1, 
  month = may, 
  pages = {1--29} 
} 
 
hth, 
Alan Isaac