MEMOIR XXIX.] CHEMICAL FORCE IN THE SPECTRUM. 435 



matter what their length may be, provided that their 

 extinction takes place without producing any chemical 

 effect. 



3d. That it is incorrect to restrict to the upper portion 

 of the spectrum the property of producing chemical 

 changes. Such changes may be produced by waves of 

 any refrangibility. 



4th. That every chemical effect observed in the spec- 

 trum is in consequence of the absorption of a specific 

 radiation, the absorbed or acting radiation being deter- 

 mined by the properties of the substance undergoing 

 change. 



5th. That the figure so generally employed in works 

 on actino-chemistry to indicate the distribution of heat, 

 light, and actinism in the spectrum serves only to mis- 

 lead. The heat curve is determined by the action of the 

 prism, not by the properties of calorific radiations; the 

 actinic curve does not represent any special peculiarities 

 of the spectrum, but the habitudes of certain compounds 

 of silver. 



