190 



POPULAR SCIENCE MONTHLY. 



GASES IN INTERPLANETARY 

 SPACE. 



The question of whether interplane- 

 tary and interstellar space is a vacuum 

 or contains matter in an exceedingly 

 attenuated form is an interesting prob- 

 lem, and one upon which there has long 

 been much speculation. On the one 

 hand the planets give no evidence of an 

 impeding friction, but on the other 

 hand the evidence of such friction in 

 the case of certain comets seems pos- 

 sible. When the earth's atmosphere 

 was supposed to consist solely of 

 oxygen, nitrogen and carbon dioxid, it 

 appeared very improbable that these 

 should pass to any considerable dis- 

 tance away from the surface of the 

 earth, but, with the more recent 

 knowledge of the constituents of the 

 atmosphere, this thesis seems less cer- 

 tain. The discovery of argon by Ray- 

 leigh and Ramsay has led to the fur- 

 ther discovery of the presence of he- 

 lium, neon, krypton and xenon, which 

 have enriched chemistry with a new 

 type of chemical element, having no 

 affinity, forming no compounds, and 

 being, as far as has yet been found, 

 perfectly inert. At the same time 

 comes the knowledge that no incon- 

 siderable quantity of hydrogen is a con- 

 stant constituent of the atmosphere. 

 This has been abundantly proved by 

 Gautier, by Dewar and by Ramsay. 

 Of these gases, hydrogen is the lightest 

 of terrestrially known elements, but 

 helium is not far behind it, and has not 

 yet been changed from its gaseous form 

 to that of a liquid. The methods which 

 have availed to condense hydrogen to a 

 liquid have thus far failed with helium. 

 Turning to the chemistry of the sun, 

 the spectroscope shows the presence of 

 an atmosphere largely of hydrogen, but 

 helium is also present, extending far 

 out from the central mass of the sun. 

 The same instrument reveals lines indi- 

 cating other elements at still greater 

 heights in the sun's atmosphere, among 

 them one which has been named coro- 

 nium. From its position far away 

 from the surface of the sun, it seems 



probable that coronium has a density 

 far less than that of even hydrogen. 

 Again, the evidence of the spectroscope 

 upon the lightest constituents of our 

 atmosphere points to the presence of 

 other gases than helium and hydrogen, 

 and this is reinforced by what the same 

 instrument shows of the aurora. The 

 latter appears to be an electric phe- 

 nomenon, concerned with elements at 

 least in part now unknown to us, and 

 at a height above the surface of the 

 earth at which it was long supposed 

 there could be no appreciable atmos- 

 phere. 



It thus appears that the upper 

 strata, both of the sun and of the 

 earth, consist of the lighter consti- 

 tuents which are largely removed from 

 the lower atmosphere by their light- 

 ness, and no limit can be placed upon 

 the distance to which these elements 

 would travel from sun or earth into 

 interplanetary space. What is true of 

 sun and earth is doubtless true also of 

 other planets and other suns, and it 

 seems not impossible that even inter- 

 stellar space may contain these and 

 similar gases in an almost infinitely 

 attenuated condition. What the con- 

 dition of these gases may be at the 

 temperature of interstellar space, 

 which cannot be far removed from 

 absolute zero, it is difficult to say. On 

 the one hand, at such a temperature 

 they might be expected to be solids, 

 but, on the other hand, the particles 

 would be relatively so few and far 

 apart from each other that they would 

 have the properties of a gas. The 

 great advance in our knowledge of 

 these fields during the last few years 

 gives promise of much new light in the 

 near future. 



THE DESTRUCTION OF FORESTS 

 BY FIRE. 

 A press bulletin from the Bureau of 

 Forestry gives an abstract of a forth- 

 coming paper entitled ' Forest Fires,' 

 by Mr. Alfred Gaskill. By impressing 

 the public with some idea of the peril 

 it suffers from forest fires, and the 



