Studies of innovation have focused on the effects of patent laws on the number of innovations, but have ignored effects on the direction of technological change. This paper introduces a new dataset of close to fifteen thousand innovations at the Crystal Palace World's Fair in 1851 and at the Centennial Exhibition in 1876 to examine the effects of patent laws on the direction of innovation. The paper tests the following argument: if innovative activity is motivated by expected profits, and if the effectiveness of patent protection varies across industries, then innovation in countries without patent laws should focus on industries where alternative mechanisms to protect intellectual property are effective. Analyses of exhibition data for 12 countries in 1851 and 10 countries in 1876 indicate that inventors in countries without patent laws focused on a small set of industries where patents were less important, while innovation in countries with patent laws appears to be much more diversified. These findings suggest that patents help to determine the direction of technical change and that the adoption of patent laws in countries without such laws may alter existing patterns of comparative advantage across countries.

Historical accounts suggest that Jewish émigrés from Nazi Germany revolutionized US science. To analyze the émigrés' effects on chemical innovation in the United States, we compare changes in patenting by US inventors in research fields of émigrés with fields of other German chemists. Patenting by US inventors increased by 31 percent in émigré fields. Regressions which instrument for émigré fields with pre-1933 fields of dismissed German chemists confirm a substantial increase in US invention. Inventor-level data indicate that émigrés encouraged innovation by attracting new researchers to their fields, rather than by increasing the productivity of incumbent inventors. (JEL J15, L65, N62, O31, O34)

Compulsory licensing allows firms in developing countries to produce foreign-owned inventions without the consent of foreign patent owners. This paper uses an exogenous event of compulsory licensing after World War I under the Trading with the Enemy Act to examine the effects of compulsory licensing on domestic invention. Difference-in-differences analyses of nearly 130,000 chemical inventions suggest that compulsory licensing increased domestic invention by 20 percent. (JEL D45, L24, N42, O31, O34)

What is the optimal system of intellectual property rights to encourage innovation? Empirical evidence from economic history can help to inform important policy questions that have been difficult to answer with modern data: For example, does the existence of strong patent laws encourage innovation? What proportion of innovations is patented? Is this share constant across industries and over time? How does patenting affect the diffusion of knowledge? How effective are prominent mechanisms, such as patent pools and compulsory licensing, that have been proposed to address problems with the patent system? This essay summarizes results of existing research and highlights promising areas for future research.

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