MOLECULAR MAGNITUDES. 653 



MOLECULAR MAGNITUDES. 



By L. R. CUKTISS. 



IN entering upon an analysis of the subject of atomic and molecular 

 masrnitudcs, it is desirable that we should have as clear an idea of 

 the immeasurably small in Nature as possible. To the astronomer the 

 size and relative distances of the celestial bodies are real magnitudes, 

 and so also, to the molecular physicist, the magnitudes verging upon 

 the infinitely small are just as much of a reality. The billionth part 

 of an inch is just as much of a fact as a billion miles. 



The mathematical definition of a point consists in stating it as a 

 locality without length, breadth, or thickness ; but we receive no very 

 concise idea of the definition until we proceed graphically, and make 

 a dot with a pencil or otherwise, which shall possess limited dimen- 

 sions of length and breadth ; then, by the metaphysical process of 

 abstraction, we dispense with the linear dimensions of length and 

 breadtli, and thus purify our conceptions concerning physical magni- 

 tudes, and place ourselves in a way of realizing the entity or real ex- 

 istence of the invisibly small in Nature. 



In the animal kingdom are found myriads of forms so minute that 

 their bulk is reckoned by less than the millionth part of a cubic inch, 

 yet each one is endowed with organs of sense or assimilation sufficient 

 to serve the purpose in their sphere of life. The vegetable kingdom, 

 also, oflTers abundant specimens of microscopic forms, calculated to 

 excite our admiration by the beauty and minuteness of their organisms. 

 Such is notably the case in several forms of Diatoinaeece. The striated 

 markings of Pleurosigma fasciola aggregate to 64,000 to the inch, 

 while Amphipleura pellucida often exhibit striae exceeding 100,000 to 

 the lineal inch. And yet the skeletons of these minute organisms are 

 composed mainly of silex, the silex again being made up of silicon 

 and oxygen. Notwithstanding the almost infinitesimal magnitudes 

 of the organic world, human skill is able to compete in the matter 

 of minuteness. Platinum wire has been drawn so fine as to rival 

 in minuteness the smallest fibre of the spider's web. Gold has been 

 deposited upon the surface of other metals, and drawn to such ex- 

 treme thinness that a thousand-millionth part of a grain exhibited 

 the visible characteristics of the metal. The oscillations of the hori- 

 zontal pendulum can be measured to the sottuWoo V'^'^^ *^^ ^"^ inch, 

 by the aid of a small mirror, a beam of light, and a graduated 

 scale for reading the vibrations. Nobert, with a mechanical skill un- 

 surpassed, has repeatedly ruled with a diamond-point upon glass the 

 nineteenth band of his test-plate, consisting of lines less than the 

 ^ ^ a'o Q ^f ^" va.Q\\ apart, and it is claimed that he has succeeded in 



