Polytechnic Asso-ciatton. 025 



change is as follows : The addition of heat causes the color to pass from 

 one of a greater to one of a less number or vibrations ; the abstraction 

 of heat from one of less to one of greater number. Yiolets are 

 changed by heat into indigo-violets, or indigoes ; indigoes into blues ; 

 blues into bluish-greens, or greens; greens into yellowish-greens, or 

 yellows ; yellows into yellow-oranges, or oranges ; oranges into orange- 

 reds, or reds ; and finally, reds into brownish-reds, or blacks. Upon 

 the application of cold the inverse order is observed. p In many 

 instances substances were noticed that ran down the scale two or more 

 colors ; for example, the green iodide of mercury passes from a vel- 

 lowish-green through the yellow and orange to the red. The experi- 

 ments prove that the waves producing heat, being slower than those 

 producing light, have a retarding effect on the latter, and change the 

 rate of oscillation ; it being previously well settled that the waves 

 producing the extreme violet have nearly doubled the velocity of 

 those producing dark red. 



Dr. Van der "Weyde said that as the heat spectrum is at one end 

 ot the light spectrum, extending beyond the red rays, it was natural 

 to expect that on heating a substance its color would go toward the 

 warmer end of the spectrum, and that on its cooling its color would 

 go back. 



Mr. Fisher — Ever since English art began, red and the neighboring 

 colors have been considered warm, while blue has been considered a 

 cold color. 



Dr. Van der Weyde — My impression is that in fact blue feels cold, 

 and red feels warm. 



Mr. R. Weir — In painting a winter scene, the artist uses different 

 tints from those used on a summer scene. He indicates the warmth 

 or the cold by the tints employed. 



Adjourned 



October 26, 1871. 



Prof. S. D. Tillman in the chair ; Robert Weir,, Esq., Secretary. 

 Dr. P. H. Van der Weyde delivered the following lecture : 



Ox THE SO-CALLED PSYCHIC FORCE. 



The so-called psychic force has lately been brought to the notice 

 of the scientific world by Mr. W. Crookes, editor of the London 

 Quarterly Journal of Science, a man favorably known among scientists 



[Ixst.] 40 



