Page:Collected Physical Papers.djvu/394

 XXIX

GENERAL SUMMARY

The investigations described in the present volume are on: A, the optical properties of electric waves; B, the characteristics of metallic-contact receivers which respond to electric radiation, either by a diminution or an increase of resistance; C, different types of molecular receivers which respond to diverse modes of stimulation; D, the similarity of response of inorganic and living substances; E, the physiological response of plants; and F, the identity of physiological mechanism in animal and plant.

Electric waves of great length curl round corners; accurate angular measurements are thus rendered impossible. The difficulty has been obviated by securing a narrow beam of electric radiation of relatively short length.

The Radiator.—Electric radiation is produced by a single spark between two hemispheres and an interposed small sphere of platinum, the wave-length being reduced to about 5 mm. The sparking coil and battery are enclosed in a small double-walled metallic box with a tube for the passage of the electric beam. Magnetic disturbance due to the make and break of the sparking coil, was found to affect the receiver; the magnetic