Page:Collected Physical Papers.djvu/8

 magnification of responsive movements, which otherwise would have been quite imperceptible. The latent period and the velocity of reaction had also to be determined with great accuracy, as also the energy of the incident stimulus.

The difficulties encountered were overcome by the successful employment of various physical methods of high sensibility and accuracy, which will be found of much service in solving not only physiological but physical problems also. A short account of some of these devices, with illustrative examples of their application, will be found towards the end of this book. The High Magnification Crescograph instantly records the imperceptible growth, and the variation induced in it under chemical or electrical stimulation. The Magnetic Crescograph records movements beyond the highest powers of the microscope, the magnification produced being about 50 million times. The Resonant Recorder inscribes time as short as a thousandth part of a second, and enables the most accurate determination of the latent or perception period of the plant and the velocity of transmission of excitation. The Photosynthetic Recorder automatically imprints on a moving drum, the rate of carbon-assimilation by plants. The Magnetic Radiometer enables relative measurement of energy of every ray of the solar spectrum. In conjunction with a special Calorimeter, a very accurate determination has been made of the efficiency of the chlorophyll-apparatus of green plants in storage of solar energy.

January, 1927.