EDITOR'S TABLE. 



627 



of a few pounds in weight, which 

 strike the earth, we have become 

 quite familiar, while spectrum analy- 

 sis has carried us a long way toward 

 the conclusion that there is a unity 

 in the material composition of the 

 universe. But, as every thing is in 

 motion, and all the celestial masses 

 are revolving and whirling at great 

 rates of speed, and, as there is much 

 evidence of fractures, collisions, and 

 transformations, it seems impossible 

 that there should not have been going 

 on constant abrasions and comminu- 

 tions, with the production of all grades 

 of dust down to the most impalpable, 

 as a consequence of the general wear 

 and tear. Such a notion would, of 

 course, have been inadmissible in old 

 times, when people reasoned about the 

 universe from their a pinori notions of 

 what it ought to be ; and, holding that 

 the heavens are the type of all perfec- 

 tion, they would have been shocked 

 at the notion that the gearing of the 

 spheres could not work without the 

 production of dirt and dust. But we 

 have survived those prejudices, and 

 now search for the celestial debris and 

 waste with just as much interest as we 

 do for more imposing and dignified 

 objects. 



It is but a few years since the 

 world was surprised and delighted by 

 that brilliant series of researches made 

 by Prof. Tyndall, on the formation of 

 artificial clouds and artificial sky by 

 the electric light, in his vacuum-tubes. 

 Spaces, washed clean, and apparently 

 pure, were found to be filthy with dust, 

 and, beginning with the thinnest trans- 

 parent vapors, he was able to develop 

 a succession of the most exquisite cloud- 

 forms definitely related to the colors of 

 the spectrum as the molecules grew in 

 complexity under the chemical trans- 

 formation. The firmamental blue he 

 found to be caused by impurities in 

 the air, so attenuated as to react only 

 with the finest waves of the ethereal 

 medium. How far down in the scale 



of minuteness beyond all previous con- 

 ception the particles are, which reflect 

 the azure light of the sky, may be gath- 

 ered from the following memorable pas- 

 sage, taken from Dr. Tyndall's '' Frag- 

 ments of Science " (page 148) : 



" From their perv'iousness to stellar light 

 and other considerations, Sir John Herscliel 

 drew some startling conclusions regarding 

 the density and weight of comets. You 

 know that these extraordinary and mys- 

 terious bodies sometimes throw out tails 

 100,000,000 of mUes in length, and 50,000 

 miles in diameter. The diameter of our 

 earth is 8,000 miles. Both it and the sky, 

 and a good portion of space beyond the sky, 

 would certainly be included in a sphere 

 10,000 miles across. Let us fill a hollow 

 sphere of this diameter with cometary mat- 

 ter, and make it our unit of measure. To 

 produce a comet's tail of the size just men- 

 tioned, about three hundred thousand such 

 measures would have to be emptied into 

 space. Now, suppose the whole of this 

 stuff to be swept together and suitably 

 compressed, what do you suppose its vol- 

 ume would be ? Sir John Herschel would 

 probably tell you that the whole mass might 

 be carted away at a single effort by one of 

 your dray-horses. In fact, I do not know 

 that he Avould require more than a small frac- 

 tion of a horse-power to remove the cometary 

 dust. After this you will hardly regard as 

 monstrous a notion I have sometimes enter- 

 tained concerning the quantity of matter in 

 our sky. Suppose a shell to surround the 

 earth at a height above the surface which 

 Avould place it beyond the grosser matter 

 that -hangs in the lower regions of the air — 

 say at the height of the Matterhom or Mont 

 Blanc. Outside this shell we have the deep- 

 blue firmament. Let the atmospheric space 

 beyond the shell be swept clean, and let the 

 sky-matter be properly gathered up. What 

 is its probable amount ? I have sometimes 

 thought that a lady's portmanteau would con- 

 tain it all. I have thought that even a gen- 

 tleman's portmanteau — possibly his snuffbox 

 — might take it in. And, whether the actual 

 sky be capable of this amount of condensa- 

 tion or not, I entertain no doubt that a sky 

 quite as vast as ours, and as good in appear- 

 ance, could be formed from a quantity of 

 matter which might be held in the hollow of 

 the hand." 



"Whatever may be the validity of 

 these quantitative speculations, all the 

 lines of investigation seem to converge 



