posed parts become dark, therefore a painting upon glass or an engraving used as a screen above such prepared paper or leather gave a copy the reverse of the superimposed design as regards light and shade.
The images given by the camera-obscura Davy found to be too faint to produce an effect upon paper prepared with nitrate of silver, but the solar microscope was used with success.
All the pictures made in this way had to be carefully preserved from daylight, or the whole surface would blacken, as a necessary consequence, and neither Wedgwood nor Davy ever overcame this difficulty, or found means to fix such photographs and render them permanent.
To Wedgwood, however, must be accorded the honor of having been the first to produce a photograph, in the artistic and technical sense of the word.
Dr. Thomas Young, the originator of the undulatory theory of light, published in 1804 some important researches on the chemical rays.
In 1809, Gay Lussac and Thenard made the exceedingly
emonstrations were regarded with much applause.
Their peculiar views on the connection of the external brain with the character met with many opponents.
In 1807, they began lecturing in Paris, and large and learned audiences sometimes listened to their expositions.
Cuvier is said to have received their system favorably at first, but to have been afterwards swayed by the haughtiness of the First Consul, who had seen with displeasure that the French Institute had awarded a prize medal to Sir H. Davy for his galvanic experiments, and at a levee rated the wise men of his land, for allowing themselves to be taught chemistry by an Englishman, and anatomy by a German.
In Paris the two lecturers began publishing.
They remained in that city until 1813.
The next year, Spurzheim went over to England, and thence to Scotland, lecturing in various places, London included.
To Edinburg he devoted seven months, the Edinburg Review having come out very strongly against him. He procured but on