CONTENTS. 



eye. Extension to photographic impressions. Encroachment on the 

 first dark space. Photographs of the diffraction spectrum. Proposal 

 to use wave-lengths for spectrum divisions. Replacement of imaginary 

 imponderable principles by wave-lengths Page 115 



MEMOIK VIII. 



ON THE PHOSPHORESCENCE OF BODIES. 



Early observations on phosphorescence. The diamond. Duration of 

 shadows. Lemery's theory. Du Fay's theory. Qualities of dia- 

 mond and fluor-spar. The volume of a phosphorescent body does not 

 change during its glow. A structural change accompanies the phos- 

 phorescence of bodies ; there is a minute disengagement of heat. Phos- 

 phorescence is not communicable. Absolute quantity of light emit- 

 ted 133 



MEMOIR IX. 



ON THE EFFECTS OF HEAT ON PHOSPHOEESCENCE. 



Experiment of Albertus Magnus. Degree of phosphorescence at different 

 temperatures. The quantity of light a substance can retain is inversely 

 as its temperature ; the quantity it can receive is directly as the inten- 

 sity and quantity of light to which it has been exposed. Phosphores- 

 cent images of the moon. Action of ether waves. Effects of cohesion. 

 Reason that gases, liquids, and metals are non-phosphorescent. . 159 



MEMOIR X. 



ON THE DECOMPOSITION OF CARBONIC- ACID GAS BY PLANTS IN THE 

 PRISMATIC SPECTRUM. 



The decomposition of carbonic acid by light formerly attributed to the 

 violet ray. It can be successfully accomplished in the prismatic spec- 

 trum. It takes place not in the violet but in the yellow ray. Decom- 

 position by yellow absorbent media. Analysis of the gas evolved ; it 

 always contains nitrogen. Decomposition of alkaline carbonates and 

 bicarbonates. Analysis of the gas evolved in different rays 167 



MEMOIR XL 



OF THE FORCE INCLUDED IN PLANTS. 



Growth of a seed in darkness and in light. Action of plants and ani- 

 mals respectively on the atmosphere. Examination of Rumford's Ex- 

 periments. Dark heat rays cannot decompose carbonic acid. Germi- 



B 



