2 20 THE POPULliR SCIENCE MONTHLY. 



proTement can be expected from other means than from skillful and 

 judicious moral intervention on the physician's part. — Iteviie des 

 Deux Mondes. 



XoTE, BY THE Editoe OF THE Reyue. — Circumstanccs have pre- 

 vented the earlier publication of the foregoing sketch, which has been 

 for some time in our possession. It is the last one sent us by one of our 

 most sympathetic fellow-laborers, whom death removed suddenly and 

 23rematurely from his friends, the 2d of January, at the age of twenty- 

 six. 



THE ATMOSPHEPwE AS AiST AKYIL.^ 



By Peofessoe J. P. COOKE, Je. 



THE office of the atmosphere, as an anvil upon which rocks are 

 shattered for the protection of humanity, has sufficient novelty 

 about it to require explanation. It has come to be pretty well under- 

 stood now that rocky fragments of all sizes are flying through space, 

 like the planets themselves. What the eflect would be, if hard me- 

 teoric stones were to strike, with a velocity sixty times as great as that 

 of a cannon-ball, the structures that man builds upon earth, it is not diffi- 

 cult to imagine. To say nothing of the larger stones, no ordinary build- 

 ings could afibrd shelter from the smallest particles striking with the 

 velocity of eighteen miles per second. Even dust flying at such a 

 rate would kill any animal exposed to it. How effectually we are 

 guarded by the atmosphere, as with a shield, impenetrable in propor- 

 tion to the violence of the assaults upon it, is admirably illustrated by 

 Prof Cooke in the following statement, condensed from Chapter X. of 

 his " Xew Chemistry :" 



" Within a few years our community have become familiar with the 

 name and terrible eff*ects of a new explosive agent, called -nitro-glyce- 

 rine, and I feel sure that you will be glad to be made acquainted with 

 the remarkable qualities and relations of this truly wonderful sub- 

 stance. Every one knows that clear, oily, and sweet-tasting liquid 

 called glycerine, and probably most of you have eaten it for honey. 

 But it has a great many valuable uses, which may reconcile you to its 

 abuse for adulterating honey, and it is obtained in large quantities, as 

 a secondary product of the manufacture of soap and candles, from our 

 common fats. Now, nitro-glycerine bears the same relation to glycer- 

 ine that saltpetre bears to caustic potash. Common saltpetre, which 

 is the oxygenated ingredient of gunpowder, is called in chemistry po- 

 tassic nitrate, and, although the commercial supply comes wholly from 

 natural sources, it can easily be made by the action of nitric acid on 



^ Condensed from " The New Chemistry," Chapter X., " Gunpowder and Kitro-Gly- 

 cerine." 



