THE RADIOMETER. 5 



from those of sugar, and so with every other substance. There are as 

 many kinds of molecules in Nature as there are different substances, but 

 all the molecules of the same substance are absolutely alike in every 

 respect. 



Thus far, as you see, we are merely reviving in a different associa- 

 tion the old ideas of Buffon. But just at this point comes in a new 

 conception, which gives far greater grandeur to our modern theory : 

 for we conceive that those smallest particles in which the qualities of a 

 substance inhere are definite bodies or systems of bodies moving in 

 space, and that a lump of sugar is a universe of moving worlds. 



If on a clear night you direct a telescope to one of the many star- 

 clusters of our northern heavens, you will have presented to the eye as 

 good a diagram as we can at present draw of what we suppose would, 

 under certain circumstances, be seen in a lump of sugar if we could 

 look into the molecular universe with the same facility with which the 

 telescope penetrates the depths of space. Do you tell me that the ab- 

 surdities of Buffon were wisdom when compared with such wild specu- 

 lations as these ? The criticism is simply what I expected, and I must 

 remind you that, as I intimated at the outset, this conception of mod- 

 ern science is in the transition period of which I then spoke, and, al- 

 though very familiar to scientific scholars, has not yet been grasped by 

 the popular mind. I can, further, only add that, wild as it may appear, 

 the idea is the growth of legitimate scientific investigation, and express 

 my conviction that it will soon become as much a part of the popular be- 

 lief as those grand conceptions of astronomy to which I have referred. 

 Do you rejoin that we can see the suns in a stellar cluster, but cannot 

 even begin to see the molecules ? I must again remind you that, in fact, 

 you only see points of light in the field of the telescope, and that your 

 knowledge that these points are immensely distant suns is an inference 

 of astronomical science ; and further that our knowledge if I may so 

 call our confident belief that the lump of sugar is an aggregate of mov- 

 ing molecules is an equally legitimate inference of molecular mechanics, 

 a science which, although so much newer, is as positive a field of study 

 as astronomy. Moreover, sight is not the only avenue to knowledge ; 

 and, although our material limitations forbid us to expect that the 

 microscope will ever be able to penetrate the molecular universe, yet 

 we feel assured that we have been able by strictly experimental meth- 

 ods to weigh molecular masses, and measure molecular magnitudes, with 

 as much accuracy as those of the fixed stars. 



Of all forms of matter the gas has the simplest molecular structure, 

 and, as might be anticipated, our knowledge of molecular magnitudes 

 is as yet chiefly confined to materials of this class. I have given below 

 some of the results which have been obtained in regard to the molecular 

 magnitudes of hydrogen gas, one of the best studied of this class of sub- 

 stances ; and, although the vast numbers are as inconceivable as are 

 those of astronomy, they cannot fail to impress you with the reality of 



