Light energy : its physics, physiological action and therapeutic applications / by Margaret A. Cleaves.

  • Cleaves, Margaret Abigail, 1848-1917.
Date:
1904
Catalogue details

Licence: Public Domain Mark

Credit: Light energy : its physics, physiological action and therapeutic applications / by Margaret A. Cleaves. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

    80/890 (page 58)
    per cent, of obscure radiation from the electric light passed through the humors of an ox's eye. The visual tract, i.e., the optic nerve and the brain, does not seem to be able to take cognizance of or respond to frequencies below the red either as light or heat. Diathermancy and Athermancy—Transmission of Ther- mal Rays.-—Diathermancy is the term used to express the power which bodies have of transmitting heat, and bears the same relation to radiant heat that transparency does to light. Athermancy, on the other hand, is the term used to express the power of stopping radiant heat and corresponds to opacity for light. A diathermanous substance is one which allows incident radiation to pass through it, apart from any consideration of the wave length of the radiation. A transparent sub- stance transmits waves of medium length, and may or may not be opaque to the very long or very short waves. A substance may be absolutely opaque and yet permit the ultra- violet or the infra-red or bofh to pass. By heat rays it is the infra-red which are generally understood. By his experiments Melloni found that calling the total radiation ioo there was transmitted as follows: Carbon bisulphide transmitted 63 Olive oil 30 Ether 21 Sulphuric acid 17 Alcohol IS Solution of alum or sugar 12 Distilled water II With solids when cut into plates 0.1 inch thick it was found that out of every 100 rays Rock salt transmitted 92 Smoky quartz 67 Transparent lead carbonate 52 Selenite 20 Alum 12 Copper sulphate o