54 MORRIS LOEB 



seventy-five different sorts of substances is a question with 

 which we cannot concern ourselves. Some chemists choose to 

 believe that they are made up of only one sort of substance, 

 arranged in different fashion for each kind of atom, and others 

 have ideas that are even more difficult to grasp than this one. 

 But inasmuch as the chemist acknowledges that he, at least, 

 cannot go further in his subdivision than the atom, it is safe 

 for us to stop there in our study this evening. We can never 

 expect to see an atom, or to distinguish it by one of our senses 

 from its neighbor. What, therefore, the real, actual proper- 

 ties of the atom may be, is just as hard for us to conceive, as 

 it is to imagine how the inhabitants of some other planet 

 would look. Nevertheless, if somebody tells us that there are 

 inhabitants of Mars, we straightway fall to imagining that 

 those Martians must look more or less like ourselves, or like 

 something that we see on earth. In the same fashion we reason 

 by analogy concerning the atoms, and readily reach conclu- 

 sions concerning their general properties from the behavior of 

 the substances which they compose. Nevertheless I would 

 especially guard those of you who are interested in chemistry 

 against imagining that we really know so very much about 

 atoms, although we know a good deal about the elements 

 after which they are named. 



Let us in the first place attempt to get some experimental 

 idea of the size of *an atom. I take here a red substance (the 

 well-known aniline dye called fuchsine) which is made up, as 

 I happen to know, of several elements; and a very little of it 

 gives, as you see, an intensely red coloration to a little water. 

 If I pour this small amount of liquid into a measuring glass, 

 and add to it one hundred times as much water, the color is 

 still very distinct, and taking one-tenth of this and again 

 diluting it with yet one hundred parts of water, you can still 

 faintly perceive the red color. Now the original weight of the 



