I think you are talking about "Equipment Investment and Economic Growth": J. Bradford DeLong and Lawrence H. Summers, "Equipment Investment and Economic Growth," Quarterly Journal of Economics 106: 2 (May 1991), pp. 445-502.(posted 8764 days ago)An electronic downloadable version of it can be found at:
http://www.j-bradford-delong.net/pdf_files/QJE_Equipment.pdf
In general, if it's written and got published somewhere, you can find a link to it from:
http://econ161.berkeley.edu/Econ_Articles/Econ_Articles.html#anchor3117498