What is the fine-grained topic of the following text: In 1939, when the electron optics laboratory of Siemens & Halske Inc. began to manufacture the first electron microscopes, the biological and medical profes­ sions had an unexpected instrument at their disposal which exceeded the reso­ lution of the light microscope by more than a hundredfold. Only return the topic.
Manufacture of the first electron microscopes in 1939 by Siemens & Halske Inc.