OP ARTS AND SCIENCES. 375 



them. This want of precise coincidence between the superimposed 

 or coinciding direct and reflex images is associated with the idea of 

 solidity, and is reproduced in stereoscopic pictures. 



Four liimdred and. seventy-seventh meeting. 



March 6, 1860. — Special Meeting. 



The President in the chair. 



Mr. E. S. Ritchie exhibited a series of experiments in Mag- 

 neto-electricity. He gave a brief account of the several steps 

 which had led to the invention of the RuhmkorfF apparatus, 

 and spoke of the effect of the condenser first introduced by 

 Fizeau, which at once converted the instrument into a pow- 

 erful source of tensional electricity. After alluding to the 

 increased energy which he had been able, by certain modifi- 

 cations, to impart to the apparatus, he proceeded to show its 

 effects by a variety of experiments, exhibiting the spark as 

 transmitted through the air, the charging of the Leyden jar, 

 the illumination of the Torricellian vacuum and of various 

 gases and vapors when greatly rarefied, and the influence of 

 the poles of a powerful magnet on these luminous discharges. 



In the course of these experiments he showed the eft'ect of 

 a current of air upon the form of the spark as first observed 

 by Du Moncel; the brilliant explosive spark of the Leyden 

 jar in the outer helix, discovered by Grove ; the common 

 and stratified discharges through a tall vacuum-tube contain- 

 ing vapor of turpentine ; the same through a tube of uranium 

 glass displaying the characteristic fluorescence ; the phenom- 

 ena of Gassiot's cascade, with the purplish fluorescence of the 

 outer glass and the green of the uranium goblet within ; the 

 various-colored light and its stratifications in the rarefied 

 gases of Geissler's Tubes ; the strong fluorescence of solu- 

 tion of sulphate of quinine when illuminated by some of 

 these lights ; the spectra furnished by others ; the attraction 

 and repulsion of a magnetic pole on the luminous strata ; 



