160 TITHONIC RAYS. INDEPENDENCE OF TITHONIC RAYS AND LIGHT. 



might be carried much farther. The powers of photography, which bring architectural 

 remains and the forms of statuary so beautifully and impressively before us, might seem 

 to be prefigured by the speaking image of the son of Tithonus and Aurora, that was 

 to be seen in the deserts of Egypt. And besides this, such words as tithonoscope, 

 tithonometer, tithonography, tithonic effect, diatithonescence, are musical in an Eng- 

 lish ear. In this paper I shall, therefore, use the term tithonicity and its derivatives in 

 the same manner that we use electricity and its derivatives. 



662. This communication takes up the consideration of three distinct facts : 

 1st. The proof of the physical independence of TITHONICITY and LIGHT. 



2d. The proof of the physical independence of TITHONICITY and HEAT. 



3d. The proof of the existence of DARK TITHONIC RAYS, analogous to the rays of 

 DARK HEAT. Under this head it will be shown that Tithonicity, like heat, enters tran- 

 siently into bodies, producing specific- changes on them, and then slowly and invisibly 

 RADIATES away. And the physical constitution of the new class of rays thus formed 

 is entirely different from that of rays that come from incandescent sources : a distinction 

 having a striking analogy in the case of heat. Tithonicity becomes transiently and 

 permanently latent in bodies. 



663. Figure 100 serves to show that by the agency of absorbent media we may 

 detect the existence of tithonic rays in every part of the spectrum unaccompanied by 

 light. The results there projected were obtained by an arrangement such as that in 

 Jig. 101. From a heliostat mirror, a a, a beam of the sun's light was thrown in a hor- 

 izontal position, and falling on a screen, b b, a portion of it passed through a circular 

 aperture one fourth of an inch in diameter. At the distance of ten or twelve feet it fell 

 on a glass trough c c, with parallel faces, into which any coloured solution could be 

 placed ; immediately behind the trough there was a double convex lens, d d, of three 

 feet focal length, and between them a second screen, ff, with an aperture correspond- 

 ing to the centre of the lens, half an inch in diameter. Behind the lens was situated 

 a prism of flint glass, e, which effected the dispersion of the incident beam. Now the 

 lens not being achromatic, the screen r v had to be placed in an inclined position in 

 order to obtain a neat spectrum-image of the hole in b b, and this was attended with 

 the great advantage of elongating the total length of the spectrum, and, therefore, in- 

 creasing the measures. In order to obtain sensitive surfaces of great delicacy, the silver 

 plates were first iodized lightly, and then exposed to the vapour of bromine until they 

 attained a full golden yellow. 



664. In Jig. 100, the line No. 1 represents the visible colorific spectrum ; it, with No. 2, 

 serves as an index of comparison for all the others. No. 2 represents the effect of a 

 spectrum that has not undergone the action of any absorbent medium on the bromo- 

 iodized plate ; the extreme red tinges the plate white, the extreme violet, brown, and all 

 the intermediate space is of a rich brownish violet, with a point of maximum action 

 nearly in its centre. The numerical subdivisions commence with at the extreme red, 

 and are graduated on a principle which I shall explain in a future paper, which makes 

 the spectrum of different tithonographists comparable. 



665. No. 3 shows the spectrum after absorption by the persulphocyanide of iron, and 



