Networks of Change: Infrastructure and Steam Diffusion in 19th-Century France

This paper examines how transport infrastructure shaped the diffusion of steam power across French departments between 1840 and 1911. Using a newly constructed annual departmental panel of steam engine stocks, firms, and installed horsepower, we reconstruct regional diffusion trajectories and estimate the causal impact of transport connectivity on mechanization. We combine department and year fixed effects with an instrumental-variable strategy based on successive French railway planning laws to address the endogeneity of railway expansion. The results reveal substantial territorial heterogeneity in the timing and speed of adoption, indicating that industrialization unfolded unevenly across space. Railway expansion exerted a positive and increasingly strong effect on steam adoption from the mid-1860s onward. An additional 100 kilometers of railway is associated with roughly six additional steam engines per 10,000 inhabitants around 1865 and more than nine by 1900. Navigable waterways also promoted adoption, though their role evolved from complementing railways to becoming progressively substituted by them as the rail network matured. To identify the mechanisms underlying these effects, we construct time-varying measures of accessibility to coal markets and engineering expertise. The results indicate that improved access to coal significantly increased steam adoption throughout the second half of the nineteenth century, while access to engineering knowledge became important only in the 1890s as steam technology grew more complex. The findings suggest that the diffusion of general-purpose technologies depended not only on relative prices and local endowments but also on the infrastructures that reduced economic and informational frictions across space.