22 



PEOFESSOR TTNDALL ON CALOEESCENCE. 



the third column the appearance of a leaf of platinized platinum when placed at the 

 focus, after the converged beam had passed through the glass, is mentioned. 



Coloiir of glass. 

 Dark red . 

 Mean red 

 Light red 



Yellow . . 

 Green . . . 



Dark purple. 

 Mean pui-ple 



Light purple 

 Dark blue 

 Mean blue . 



Light blue . 



Another blue glass 

 Black glass No. 1 



Black glass No. 2 

 Black glass No. 3 



Prismatic examination. 

 Red only transmitted ...... 



Red only transmitted 



Yellow intercepted with greatest power 



All the blue end absorbed .... 



( Besides the green, a dull red fringe and a 1 

 I blue band were transmitted . . . . j 



Extreme blue and red transmitted . 



Central portion of spectrum cut out . 

 J Dims the whole spectrum, but chiefly ab- 1 

 I sorbs the green J 



{Transmits the blue, a green band, and a 1 

 band in the extreme red J 



f Blue ; a yellowish-green band and the ex- 1 



I treme red transmitted J 



' Transmits a series of bands — blue and 

 green, a red band next orange, then a 

 dark-red band, and finally extreme red 



Calorescence. 

 Dull white heat. 

 White heat. 

 Bright white. 

 Vivid red with bright 

 yellow in centre. 



No incandescence. 



Vivid orange. 

 Vivid orange. 



Vivid orange. 



{Dims all the spectrum : white light trans- 

 mitted . 



Whitish-green light transmitted . . . 



Deep-red light transmitted 



Red heat. 

 Reddish-pink heat. 



Pink heat, passing 

 into red. 



Pink heat. 



Barely visible red. 



Dull red. 



Bright red, orange in 

 the middle. 



The extremely remarkable fact here reveals itself, that when the beam of the electric 

 lamp is sifted by certain blue glasses, the platinum at the focus glows with a distinct pink 

 colour. Every care was taken to avoid subjective illusion here. The pink colour was also 

 obtained at the focus of invisible rays. Withdrawing all the glasses, and filtering the 

 beam by a solution of iodine alone, platinum was raised nearly to whiteness at the 

 focus. On introducing the pale-blue glass between the iodine cell and the focus, the 

 calorescence of the platinum was greatly enfeebled — so much so, that a darkened room 

 was necessary to bring it out in full distinctness ; when seen, however, the thermograph 

 was pink. A disk of carbonized paper being exposed at the obscure focus, rose at once 

 to vivid whiteness when the blue glass was absent ; but when present, the colour of the 

 light emitted by the carbon was first a distinct pink ; the attack of the atmospheric 

 oxygen soon changes this colour, the combustion of the carbon extending on all sides 

 as a white-hot circle. If subsequent experiments should confirm this result, it Avould 



