SCIENTIFIC SIDE-LIGHTS 



Atmosphere 

 Atoms 



whose diameter is at least double, and its 

 bulk therefore sevenfold that of the central 

 globe. YOUNG The Sun, ch. 6, p. 191. (A., 

 1898.) 



274. ATMOSPHERE ONCE A SOURCE 

 OF ERROR Combustion Not Understood till 

 a Century Ago. At first sight chemical 

 processes are frequently very obscure, and 

 one great reason is, that we live in an at- 

 mosphere which is a mixture of two in- 

 visible aeriform substances, named nitrogen 

 gas and oxygen gas; and these substances, 

 especially the last, are constantly entering 

 as factors into chemical processes without 

 our noticing the circumstance; and, again, 

 the products of such processes, when aeri- 

 form, often escape notice by mingling with 

 the great volume of the air. Now, that we 

 are on our guard, we are seldom deceived by 

 the intervention of the atmosphere; but in 

 former times, when the qualities and rela- 

 tions of aeriform bodies were little known, 

 so great was the obscurity thus caused 

 that even the familiar processes of com- 

 bustion have not been understood until 

 within a century. COOKE New Chemistry, 

 lect. 4, p. 87. (A., 1899.) 



275. ATMOSPHERE, POSSIBLE, OF 



THE MOON Upon the whole, then, there 

 may (and there should) exist on the moon 

 an atmosphere of feeble density, and prob- 

 ably of a composition very different from 

 ours. Perhaps there may also exist certain 

 liquids, such as water, but in a minimum 

 quantity. If it had no air at all there 

 could not exist a single drop of water, see- 

 ing that it is the atmospheric pressure 

 which maintains water in the liquid state, 

 and that without it all water would imme- 

 diately evaporate. It is possible, after all, 

 that the lunar hemisphere which we never 

 see may be richer in fluids than the visible 

 one. But we see that in any case it would 

 be contrary to the real interpretation of 

 facts to assert, as is too often done, that 

 there is absolutely no atmosphere nor any 

 liquid or fluid on the surface of the moon. 

 FLAMMABION Popular Astronomy, bk. ii, 

 ch. 4, p. 140. (A.) 



276. ATMOSPHERE SEPARATED IN- 

 TO STRATA WOULD DESTROY PITCH 

 OF SOUNDS Music Depends on Chemical 

 Law Diffusion of Gases. As the air is now 

 constituted, there is a constancy of pitch, 

 however far sound travels. Any tone once 

 generated remains the same tone until it 

 dies away. Its degree of loudness alters 

 in proportion to the distance of the listener, 

 but the pitch is constant. Were it not, 

 however, for this law of diffusion were the 

 atmosphere not perfectly homogeneous, and 

 the gases of which it consists even partially 

 separated there would have been a very 

 different result. The constancy of pitch 

 could no longer have been depended upon. 

 The sound as it traveled would vary its 

 pitch with the ever-varying medium 

 through which it passed, and would arrive 



at the ear with a tone entirely different 

 from that with which it started. Nor 

 would it require any great difference in the 

 medium to produce a sensible result and to 

 confuse all those delicate differences of 

 pitch on which the whole art of music de- 

 pends. Whenever, therefore, you may be 

 next enjoying the grand Pastoral Symphony 

 of Beethoven or the Requiem of Mozart, re- 

 call the careful adjustment of forces by 

 which alone these magnificent creations of 

 genius were rendered possible, and you can- 

 not fail to recognize in this Dimple law of 

 Nature the same hand that first strung the 

 lyre and made the soul of man responsive 

 to its seven notes. COOKE Religion and 

 Chemistry, ch. 3, p. 76. (A., 1897.) 



277. ATOMS FALL TOGETHER IN 

 COMBUSTION The burning of charcoal 

 in oxygen is an old experiment, but it has 

 now a significance beyond what it used to 

 have; we now regard the act of combina- 

 tion on the part of the atoms of oxygen and 

 coal as we regard the clashing of a falling 

 weight against the earth. The heat pro- 

 duced in both cases is referable to a com- 

 mon cause. A diamond, which burns in 

 oxygen as a star of white light, glows and 

 burns in consequence of the falling of the 

 atoms of ogygen against it. TYNDALL 

 Fragments of Science, vol. i, ch. 16, p. 372. 

 (A., 1897.) 



278. ATOMS, POLARITY OF Every 

 Fragment of the Magnet Retains Its Poles. 

 What, then, will occur if we break this 

 magnet in two at the center? Shall we ob- 

 tain two magnets, each with a single pole? 

 No; each half is in itself a perfect magnet, 

 possessing two poles. This may be proved 

 by breaking something of less value than 

 the magnet the steel of a lady's stays, for 

 example, hardened and magnetized. It acts 

 like the magnet. When broken, each half 

 acts like the whole; and when these parts 

 are again broken we have still the perfect 

 magnet, possessing, as in the first instance, 

 two poles. Push your breaking to its ut- 

 most sensible limit, you cannot stop there. 

 The bias derived from observation will in- 

 fallibly carry you beyond the bourn of the 

 senses, and compel you to regard this thing 

 that we call magnetic polarity as resident 

 in the ultimate particles of the steel. You 

 come to the conclusion that each atom of 

 the magnet is endowed with this polar force. 

 TYNDALL Lectures on Light, lect. 3, p. 97. 

 (A., 1898.) 



279. ATOMS, THEIR NUMBER AND 

 WEIGHT Heat a Peculiar Form of Atomic 

 Motion. Chemistry teaches that heat is 

 directly related to the atoms of matter. 

 Atoms of different substances differ greatly 

 in weight. For instance, the hydrogen atom 

 is the unit of atomic weight, because it is 

 the lightest of all of them. Taking the hy- 

 drogen atom as the unit, in round numbers 

 the iron atom weighs as much as 56 atoms 



