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IX. The Bakerian Lecture. — On Repulsion resulting from Radiation . — Part V. 
By William Crookes, F.R.S., V.P.C.S., &c. 
Received December 3, 1877, — Read January 17, 1878. 
Contents. 
Par. 
Introduction 220 
Multiple disk torsion apparatus 221 
Action of radiation on various powders .... 224 
Effect of a water screen on radiation 224 
Comparison between — 
Lampblack and black powders 224 
Lampblack and white powders 225 
Lampblack and red powders 226 
Lampblack and brown powders 227 
Lampblack and yellow powders 228 
Lampblack and green powders 229 
Lampblack and blue powders 230 
Lampblack and dyes and colouring matters 
of organic origin 231 
Lampblack and metals 232 
Lampblack and palladium — hydrogen alloy 233 
Lampblack and silver salts 234 
Lampblack and silver salts after exposure 
to light 235 
Lampblack and selenium, crystalline and 
vitreous 236 
Lampblack and miscellaneous substances, 
pith, charcoal, glass, &c 237 
Action of radiation on charcoal of various kinds 239 
Apparent viscosity of a vacuum 240 
Effect of screens 241 
Different actions of radiant heat and of light 242 
Positive and negative substances 242 
Experimental verification of theory 244 
Apparatus for testing anomalous couples .... 244 
Chromic oxide and precipitated selenium . . 245 
Chromic oxide and copper tungstate 246 
Persulpho-cyanogen and copper oxalate . . . 247 
Persulpho-cyanogen and saffranin 248 
Saffranin and zinc oxide 249 
Barium sulphate and calcium carbonate ... 250 
Thallic oxide and green platinum salt of 
Magnus 251 
Various metallic couples 252 
2 
Par. 
Anomalies exhibited by selenium 255 
Experiments with polarised light 259 
Effect of shape in influencing the amount and 
direction of repulsion 264 
Special experiments with sloping- vaned radio- 
meters 273 
Different behaviour of thick and thin mica 
flies 277 
Action of light and heat on aluminium 278 
Contradictory results when dark heat acts on 
sloping-vaned radiometers 282 
Negative rotation on heating polar portions of 
radiometers 298 
Positive rotation on heating equatorially .... 299 
Opposite rotation of aluminium and of thin 
mica flies, when cooling. . . 308 
Action of radiation on cones 309 
Apparent attraction towards the light 310 
Action of radiation on cylinders 314 
Action of radiation on cups 318 
Effect of lampblack on gold and aluminium cups 319 
Effect of cutting off radiation from one or the 
other side 322 
Effect of over exhaustion on a radiometer. . , . 334 
Point of maximum sensitiveness 334 
Experiments with dark and luminous heat 
applied internally 336 
Negative rotation at low exhaustions 341 
Internal heat radiometer 344 
Improved mercurial pump 355 
Apparatus for measuring the viscosity of air 
and gases 356 
Effect of air currents 364 
Connexion between viscosity, pressure, repul- 
sion by radiation, and rotation of the moving 
disks and vanes, in air 365 
Do. do. in hydrogen 378 
Diagram of curves, showing results in air. . . . 383 
Definitions of a “ vacuum” 385 
I 2 
