MR. W. CROOKES OK REPULSION RESULTING FROM RADIATION. 
2G9 
The phenomena observed with this couple are similar to those commented on in 
the case of the chromic oxide and copper tungstate (246). The explanation there given 
will apply equally well to the present case. 
248. Another couple was now tried, namely — 
No screen. 
Water screen. 
Persulpho-cyanogen 
. . 43-9 
1-0 
Saffranin . . 
. , 41-0 
4-3 
+ 2*9 
-3-3 
Tested in the same way as the others the results were in conformity with the 
figures. Positive rotation (persulpho-cyanogen being repelled) was obtained when 
exposed to the naked flame, and negative rotation (saffranin repelled) when water 
was interposed. In either case the movement was feeble, and was not continuous 
with only one candle. With two or three candles the rotations were strong. 
249. Another couple (saffranin and hydrated zinc oxide) were now selected, which 
were nearly equal to the naked flame but different behind water. The figures are — 
No screen. 
Water screen. 
Saffranin 
. . 41-0 
4-3 
Hydrated zinc oxide 
. . 40‘5 
1-2 
+ 05 
+ 3-1 
Tested as in the other experiments, no motion could be detected with the naked 
flame of one candle, and only slight repulsion of the saffranin when five candles were 
used. Behind water, however, there was good rotation with one candle, the saffranin 
being repelled. 
Upon inverting, a hot glass shade over the bulb no movement of the fly was 
produced. 
250. A couple was now selected which should give rotation to the naked flame, but 
none behind water. They were — 
Barium sulphate 
Calcium carbonate 
No screen. Water screen. 
37-4 0-3 
28-5 0-3 
+ 8-9 0-0 
With no screen, good rotation was produced, the barium compound being repelled. 
No movement whatever was observed when a water screen was interposed. 
Covered with a hot glass shade rotation was produced, the barium sulphate being 
repelled. There was slight reversion of movement on cooling. 
