Triumphs and wonders of the 19th century, the true mirror of a phenomenal era, a volume of original, entertaining and instructive historic and descriptive writings, showing the many and marvellous achievements which distinguish an hundred years of material, intellectual, social and moral progress .. . n its relations toagriculture has shown that the fertil-ity of the soil may be conserved andincreased, while the magnitude of thecrops harvested is sustained or aug-mented. Thus, no matter how rapidmay be the increase of population, agri-cultural chemistry will provide abun-dant food. VIII. GRAPH
Triumphs and wonders of the 19th century, the true mirror of a phenomenal era, a volume of original, entertaining and instructive historic and descriptive writings, showing the many and marvellous achievements which distinguish an hundred years of material, intellectual, social and moral progress .. . n its relations toagriculture has shown that the fertil-ity of the soil may be conserved andincreased, while the magnitude of thecrops harvested is sustained or aug-mented. Thus, no matter how rapidmay be the increase of population, agri-cultural chemistry will provide abun-dant food. VIII. GRAPHIC CHEMISTRY. The honor of discovering that printscould be made by the action of light oncertain salts, such as those of silver,belongs to Daguerre, in 1839. The fundamental principle of graphicchemistry is that metallic salts, sensi-tive to the light, when in contact withorganic matter, suffer a complete orpartial reduction and are rendered in- louis jacques daguekre soluble. The intensity of the reduc-tion is measured exactly by the intensity of the light. When light isreflected from any object capable of producing different degrees of intensity,as from the hair and face of a man. the reduction of the metal is greatestby the light from that portion of the physiognomy which gives the greatest. 204 TRIUMPHS AND WONDERS OF THE XIX™ CENTURY reflection. Thus, when the unreduced metallic salt is washed out, a perma-nent record, the negative, of the object is left. It is a long step from the first daguerreotype to the modern photograph,but the principle of the process has remained unchanged. Photographs in natural colors have of late years been obtained. Onemethod is by interposing a film of metallic mercury behind the sensitiveplate which must be transparent. The reflected rays of light, having differ-ent wave lengths, precipitate the metal in superimposed films, correspondingto the wave or half-wave length. When a negative thus formed is seen byreflected light, the emergent rays
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Keywords: ., bookcentury1800, bookdecade1890, bookidtri, booksubjectinventions
