108 Scientific Intelligence. 
- surpass rock crystal in diactinic power. Water, ice and white fluor spar 
rival it, and pure rock salt approaches it very closely. With respect to 
saline bodies, it was found that the flworids rank first in diactinic power 
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the phosphates less so, and the arseniates still less. .The sulphites are 
ess diactinic than the sulphates, and the hyposulphites less than the sul- 
phites. Nitric acid and the nitrates exert a specific absorptive action, 
interrupting the spectrum abruptly at the same point whatever be the 
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refrangible rays almost as completely as a plate of twenty times the 
thickness. Of the liquids examined, water is most diactinie, and next 
in order aleohol. Among gases, air, hydrogen, carbonic acid, carboni¢ 
oxyd and ammonia are about equally diactinic with each other and with 
water. Other gases and vapors exhibit a marked absorptive power, and 
this is especially the case with the compounds of sulphur. Chlorine, 
bromine and iodine absorb most powerfully the least refrangible rays, 
which is an exception to the general rule; peroxyd of nitrogen and 
oxyd of chlorine in a stratum two feet in length wholly absorb the che- 
mical rays; but when more dilute or in shorter columns, they give pecu- 
liar absorption bands. Aqueous vapor is highly diactinic, though not , 
diathermic. 
The reflecting power of different polished surfaces for the chemical 
rays was found to be very different for different substances, for the same 
angle of reflection. Gold reflects all the rays very equally, though some- 
what feebly, and next to gold ranks burnished lead. These two metals 
reflect all the light of the silver-spectrum, or 74 divisions of the authors 
scale, while with other metals the reflected spectrum covered only 63 
divisions of the same scale. In examining the electric spectra of differ- 
ent metals taken in air, the author found that as we advance toward . 
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ends alone are visible, so as to give the appearance of two dots of 
