88. Rectilinear Propagation of X-rays ROENTGEN Indicated by Pin-hole Camera and Sharpness of Sciagraphs. 89. Interference Uncertain Because X-rays ROENTGEN Tested were Weak. 90. Electrified Bodies, whether Conductors ROENTGEN or Insulators, or Positive or Negative, Discharged by X-rays. Hydrogen, etc., as the Intermediate Agency. 90_a_. Application of Principle of Discharge ROENTGEN by X-rays. 90_A_, Supplementary Experiments on Charge and MINCHIN, _b_, Discharge by X-rays. RIGHI, _c_, BENOIST, _d_. HURMUZESCU, and BORGMANN 91. Focus Tube. ROENTGEN, SHALLENBERGER, _et al._ 91_a_. Tribute to the Tesla Apparatus. ROENTGEN 92. X-rays and Longitudinal Vibrations. ROENTGEN 93. Longitudinal Waves in Luminiferous THOMSON Ether by Electrical Means Early (KELVIN) Predicted by 94. Theory as to X-rays Being of a SCHUSTER Different Order of Magnitude from those so far Known. 95. Longitudinal Waves Exist in a Medium THOMSON, J. J. Containing Charged Ions. Theoretical. 96. Practical Application of X-rays BOLTZMANN Foreshadowed. 97. The Sciascope. MAGIE, SALVIONI, _et al._ CHAPTER VIII. 97_a_. Electrified Bodies Discharged by Light HERTZ of a Spark, and the Establishment of a Radical Discovery. 97_b_. Above Results Confirmed and More WIEDEMANN and Specific Tests. EBERT 98. Negatively Charged Bodies Discharged by ELSTER and Light. Discharge from Earth’s Surface GEITEL Explained by Inference and Experiment. 99. Relation between Light and Electricity. ELSTER and Cathode of Discharge Tube Acted upon GEITEL by Polarized Light and Apparently Made a Conductor Because of the Discharging Effect.