1878.] On Repulsion resulting from Radiation. 



85 



Summary. 



Series. 



1 



2 

 3 

 4 



(B + X)- 

 (A+X)- 

 (A+X)- 

 (B+X)- 



(A+T) 

 (B + Y) 

 (B + Y) 

 (A+Y) 



Mgms. 



0718 

 1610 

 1732 

 1500 



Greatest deviation 

 from mean in 

 milligrammes. 



A=B + -0446 mem. 



0067 J 

 00571 

 0122 J 



A=B + -0116 mgm, 



5 (B+Y)- 



6 (B+X)- 



7 (B + Y)- 



8 (B+X) 



(A + X) 

 (A + Y) 

 (A + X) 

 (A+Y) 



0065 

 4043 

 1283 

 4119 



2} B=A+-198 9 mgm . 

 S} B=A + -1418 mgm . 



The greatest error — that is the greatest deviation of any one value 



from the mean of its series — in the first four series is 

 pound. The greatest error in the four series Nos. 5— 

 of a pound. 



20000000 



th Of 



1S 50000000^ 



II. " On Repulsion resulting from Radiation." Part VI. By 

 William Crookes, F.R.S., V.P.C.S. 



(Abstract.) 



In this part, with which the research closes, the author first examines 

 the action of thin mica screens fixed on the fly of an ordinary radio- 

 meter, in modifying the movements. It is found that when a disk 

 of thin clear mica is attached 1 millim. in front of the blacked side of 

 the vanes of an ordinary radiometer, the fly moves negatively, the 

 black side approaching instead of retreating from the light. When 

 a thin mica disk is fixed on each side of the vanes of a radiometer, 

 the result is an almost total loss of sensitiveness. 



In order to examine the action of screens sfcill further an instru- 

 ment is described having the screens movable, and working on a pivot 

 independent of the one carrying the fly, so that the screens can move 

 freely and come close either to the black or to the white surfaces of the 

 disks. By gentle tapping the screens can be brought within 2 millims. 

 of the black surfaces. A candle is now brought near, shaded so 

 that the light has to pass through one of the clear disks and fall on 

 the black surface. The black side immediately retreats, the clear 

 disk remaining stationary for a moment and then approaching the 

 light. If the candle is allowed to shine on the plain side of the black 

 disk, no immediate movement takes place. Very soon, however, both 

 disks move in the same direction away from the candle, the speed of 

 the clear disk gradually increasing over that of the blacked disk. 



