1878.] 



resulting from Radiation. 



31 



when a water screen is interposed the action becomes 69*5, in com- 

 parison with standard lampblack = 100. Omitting selenium, the mean 

 action on red powders without a water screen is 32*2, and with a water 

 screen, 24*9. 



Table IV gives the brown powders. Amongst these, peroxide of 

 thallium is remarkable as being repelled under the influence of radia- 

 tion to a greater extent than any other body hitherto examined, its 

 value being 1217, in comparison to lampblack = 100. Brown powders 

 behave most like black, the averages of the columns without and with a 

 water screen being 92*7 and 94*5. 



Table Y gives the yellow powders. Among these anhydrous tungstic 

 acid resembles scarlet selenium in its anomalous action, the figures 

 being without water 50 - 8 &n.& with water 72*2. The averages of the 

 other yellow powders are 35' 7 and (behind water) 13*8. 



Table VI gives green powders. These show some discrepancies, 

 which will be referred to farther on. 



Table VII gives the blue powders. The action on these is of 

 interest, as showing a much stronger proportionate action behind a 

 water screen than with no screen, the averages being 55'8 and 65'2. 



Table VIII gives the action on dyes and colouring matters of organic 

 origin. Among these may be noticed saffranin, and a product of the 

 decomposition of chlorophyll, which act differently to the others. 



Table IX gives the action on metals prepared in different ways and 

 coated with lampblack, mica, &c. Curious results are shown with iron 

 and with gold, the former metal chiefly absorbing the invisible heat 

 rays, whilst the latter metal is principally acted on by the luminous 

 rays. 



Tables X and Xa give the results of an examination of various 

 silver salts in their sensitive and non-sensitive state to light. The 

 chloride, bromide, and iodide of silver, in their different states, are 

 exposed to the standard candle after being submitted to the action of 

 magnesium light, sunlight, and daylight. The results show how 

 readily a change in the state of the surface is detected by an increased 

 amount of repulsion under the influence of radiation. 



Table XI gives the results of an examination of selenium disks. 

 These are of two kinds, the vitreous and the crystalline. The latter is 

 in the state most sensitive to light action. With the crystalline disk 

 results have been obtained which seem to show that the impact of 

 light on its surface produces a superficial disturbance there and in the 

 adjacent gaseous molecules, which takes some time to subside. This 

 is connected with the change in electric conducting power of crystal- 

 line selenium — a change which, when the element is transferred from 

 light to darkness, takes some time to subside. 



Table XII gives the results of the action of radiation on various 

 substances which do not come under any of the foregoing headings, 



