ON RADIANT MATTER. 



165 



the metal is now -white-hot. I increase the intensity of the sj^ark. The 

 iridio-platinum glows with almost insupportable brilliancy, and at last 

 melts. 



The Chemistry of Radiant JIatter.— Fig. 21. 



As might be expected, the chemical dis- 

 tinctions between one kind of radiant mat- 

 ter and another at these high exhaustions 

 are difficult to recognize. The physical 

 properties I have been elucidating seem 

 to be common to all matter at this low 

 density. Whether the gas originally un- 

 der experiment be hydrogen, carbonic acid, 

 or atmospheric air, the phenomena of phos- 

 phorescence, shadows, magnetic deflection, 

 etc., are identical, only they commence at 

 different pressures. Other facts, however, 

 show that at this low density the mole- 

 cules retain their chemical characteristics. 

 Thus by introducing into the tubes appro- 

 priate absorbents of residual gas, I can see 

 that chemical attraction goes on long after 

 the attenuation has reached the best stage 

 for showing the phenomena now under 

 illustration, and I am able by this means to 

 carry the exhaustion to much higher de- 

 grees than I can get by mere pumping. Working with aqueous vapor, 

 I can use phosphoric anhydride as an absorbent ; with carbonic acid, 

 potash ; with hydrogen, palladium ; and with oxygen, carbon, and 

 then potash. The highest vacuum I have yet succeeded in obtaining 

 has been the ^-o.o-oV.Tro o^ ^^ atmosphere, a degree which may be bet- 

 ter understood if I say that it corresponds to about the hundredth of 

 an inch in a barometric column three miles hish. 



It may be objected that it is hardly consistent to attach primary 

 importance to the presence of matter, when I have taken extraordinary 

 pains to remove as much matter as possible from these bulbs and these 

 tubes, and have succeeded so far as to leave only about the one mil- 

 lionth of an atmosphere in them. At its ordinary pressure the atmos- 

 phere is not very dense, and its recognition as a constituent of the 

 world of matter is quite a modern notion. It would seem that, when 

 divided by a million, so little matter will necessarily be left that we 

 may justifiably neglect the trifling residue, and apply the term vacuum 

 to space from which the air has been so nearly removed. To do so, 

 however, would be a great error, attributable to our limited faculties 

 being unable to grasp high numbers. It is generally taken for granted 

 that when a number is divided by a million the quotient must neces- 



