562 
MESSRS. W. SPOTTISWOODE AND J. FLETCHER MOULTON 
Page. 
Effects on phosphorescence dne to the size of the negative terminal. 586 
Experiments on pressure, and on the distance from source at which phosphorescence can be 
produced.. .. 587 
Phosphorescence due to concentration of streams by a magnet. 588 
Effect of molecular streams on thin films of glass lying loosely in the tube. 588 
Retardation of streams by pressure of gas. 589 
Importance of streams in the process of the research ... 591 
Section XVIII .—The sensitive state exists in discharges through tubes of high exhaustion when the current 
has the sharp intermittence which is the essential condition of its existence in tubes of lower 
exhaustion. 
Sensitiveness in residual haze...... 592 
Sensitiveness in phosphorescent phenomena ... 592 
Connexion between sensitiveness and intermittence in high vacua. 594 
Section XIX.— When the air-spark is in the positive the discharge passes through the tube in the shape 
of positive electricity , and vice versa. 
Experiments on the residual haze ...... . .. 596 
Unipolar effects produced in an auxiliary tube. 596 
Application of standard-tube method with positive air-spark. 598 
Application of same method with negative air-spark . 598 
Comparison of results in tubes of high vacua with those in tubes of low vacua. 599 
Section XX .—Phosphorescence exists in sensitive as well as in continuous discharges; and when occur¬ 
ring in sensitive discharges it is intermittent in a like manner with the other luminous effects. 
Observations with a revolving mirror ... 599 
Experiment with radiometer... 600 
Phosphorescence to be treated separately from the discharge proper. 601 
Section XXI .—On the relief-effects in tubes of high exhaustion with a positive air-spark. —J, Relief- 
phosphorescence. 
Relief-phosphorescence described. 602 
Due to action at bounding surface of terminal and gas . . 603 
Produced with double unipolar arrangement. 603 
Also in tube with two terminals near together. 603 
Direction and source of relief streams indicated by shadows... 604 
Direction not strictly normal to relieving surface... 604 
Form of phosphorescent figure due to— 
A longitudinal strip . 606 
A transverse strip, or ring . 606 
A helix. 607 
Interference of molecular streams . 609 
Section XXII .—On the relief-effects in tubes of high exhaustion with a positive air-spark. — II. Virtual 
shadows. 
Definition of a virtual shadow..... 610 
Virtual shadows due to the beating dawn of molecular streams which come from the negative 
terminal . 611 
Interference by relief phosphorescence from a point opposite the end of a negative terminal .. 612 
Bulging of shadows of conductors within the tube due to counter-streams from the conductors 613 
Absence of bulging with non-conducting objects within the tube. 614 
Virtual shadows when there are small phosphorescent objects within the tube . 615 
Proof that virtual shadows are directed from the negative, not towards the positive terminal. . 615 
