548 THE POPULAR SCIENCE MONTHLY. 



toniical elements from which direct analysis extracts a certain number 

 of chemical principles. Here the anatomist's work ends. The chemist 

 steps in, and recognizes in these principles definite kinds arising from 

 the combination, in fixed and determinate proportions, of a certain 

 number of principles that cannot be decomposed, substantially in- 

 destructible, to which he gives the name of simple bodies. Carbon, 

 nitrogen, oxygen, hydrogen, sulphur, phosphorus, calcium, iron, which 

 thus set a limit to experimental analysis of the most complex bodies, 

 are simple substances, that is to say, they are the original and irresolv- 

 able radicals of the tissue of things. 



We now know that matter is not indefinitely divisible, and that 

 the smallest parts of the various simple substances existing in those 

 that are naturally compound have not all the same dimensions, nor 

 equal weights. Chemistry, by a course of analyses and measurements, 

 has succeeded in determining the weights of atoms of the different 

 elements, that is to say, taking as a unit an atom of the lightest 

 element, hydrogen, in determining the weight of the atoms which are 

 equivalent to this conventional unit in the various combinations. 

 Though many savants continue to maintain that atomic weights are 

 nothing but relations, and that the existence of atoms is a mere logi- 

 cal device, it seems more reasonable to admit, with the majority of 

 those who have studied this difficult problem closely, that these atoms 

 are actual realities, w r hile it may be very far from easy to settle pre- 

 cisely their absolute dimensions. In any case, we may affirm that 

 these dimensions are very much less than those presented by the par- 

 ticles of matter subjected to the most powerful and subtle methods of 

 division, or decomposed by the imagination into its minutest elements. 

 " Let man," says Pascal, " investigate the smallest things of all he 

 knows ; let this dot of an insect, for instance, exhibit to him in its 

 diminutive body parts incomparably more diminutive, jointed limbs, 

 veins in those limbs, blood in those veins, in that blood humors, and 

 drops within those humors let him, still subdividing these finest 

 points, exhaust his power of conception, and let the minutest object 

 his fancy can shape be that one of which we are now speaking 

 he may, perhaps, suppose that to be the extreme of minuteness in 

 Nature. I will make him discover yet a new abyss within it. I 

 will draw for him not merely the visible universe, but all besides 

 that his imagination can grasp, the immensity of Nature, within the 

 confines of that imperceptible atom." In this Pascal displays a feel- 

 ing as true as it is deep of the infinitely small, and it is interesting to 

 observe how the amazing revelations of the microscopic world have 

 justified his eloquence and foresight; and yet this microscopic world, 

 whose minutest representatives, such as vibrios and bacteria, are hard- 

 ly less than the ten-thousandth part of -^ of an inch, how coarse it is 

 compared with the particles thrown off by odorous bodies, and with 

 the inconceivably minute quantities which chemistry, physics, and 



