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Chemistry and Physics. 481 
Radiometer.—in recent numbers of Mature (April 3rd and 
April 10th, 1879), Mr. W. Crookes gives an abstract of his later 
researches on the “ Repulsion aisles from Radiation.” He 
Interposed, and also when a cell of water was inserted in the path 
of the rays; and the difference in Ane relative effects under these 
conditions is very striking. These phenomena, which are similar 
to those seep saris wae Melloni. under the name of “ ene 
the water-screen was inte eit was only one-twelfth of that ex- 
erted by the standard candle flame when no screen in the 
way, the distance of the candle and other things being of course 
equal. With the effect on the standard lamp-blacked disk the 
other repulsions were compared and hence if the direct effect of . 
the source employed on this disk is arbitrarily expressed by the 
number 100, the effect of the same source on the same disk through 
r 
pressed by the number 8°3. The other numbers of the following 
table have a similar meaning. 
eee screen Per ego ict biog 
No screen. rposed. water 
Lampblack Jogpeceat Bs alee 100° “8 3 100° 
Chromic oxide (pale green), --.-- 715 17 20°74 
Coppe’ ALG. ig cna ees 51:2 6°4 76°8 
Prosulphocyanogen, -..--.----- 43°9 1-0 12°0 
Sa Soc 41-0 43 51°6 
Hydrated zinc oxide, 40°5 1°2 14:4 
Barium sulphate. 2. <i. ...cs- B74 0°3 
Selenium precipitated, peas ues 35°8 5°8 69°6 
Copper 30°1 3°3 396 
Calcium carbonate, geecicisscs Ae 28-5 03 3°6 
It appears from pale me that the substances experimented on 
may be divided into 
(1.) Negative: Choe 1 in which the repulsion behind water bears 
a greater proportion to the standard than when no screen is inter- 
PEs. ) Positive: those in which the repulsion behind water bears a 
less proportion to the standard, than when no screen is interposed, 
Amongst Class 1, are copper tungstate, saffranin, selenium and 
copper oxalate. Amongst Jlass 2, chromic oxide, persulphocy- 
anogen, hydrated zinc oxide, barium sulphate and calcium carbo- 
nate. Evidently these differences must corres pond to a difference 
in the capacity of coals Se the luminous and ats non-luminous 
Am. Joor. Scr. San 2 p Series, Vou. XVII, No, 102.—Junz, 1 
