NA TURE 



[November 25, 1922 



The Atoms of Matter ; their Size, Number, and Construction. 1 

 By Dr. F. W. Aston, F.R.S. 



THAT matter is discontinuous and consists of 

 discrete particles is now an accepted fact, but 

 it is by no means obvious to the senses. The surfaces 

 of clean liquids, even under the most powerful micro- 



ns,™ 0.001 mm 



Yeast Human Hair Thinnest Wo/hston Influenza Bacll, 



Wire or Quartz Fibre 



Fig. 1. — Cubes n to 15 compared with familiar objects to scale. 



scope, appear perfectly smooth, coherent, and con- 

 tinuous. The merest trace of a soluble dye will colour 

 millions of times its volume of water. It is not sur- 

 prising, therefore, that in the past there have arisen 

 schools which believed that matter was quite continuous 

 and infinitely divisible. 



The upholders of this view said that if you took a 

 piece of material, lead, for example, and went on cutting 

 it into smaller and smaller fragments with a sufficiently 

 sharp knife, you could go on indefinitely. The opposing 

 school argued that at some stage in the operations 

 either the act of section would become impossible, 

 or the result would be lead no longer. Bacon, Descartes, 

 Gassendi, Boyle, and Hooke were all partial to the 

 latter theory, and Newton in 1675 tried to explain 

 Boyle's Law on the assumption that gases were made 

 up of mutually repulsive particles. 



The accuracy of modern knowledge is such that we 

 can carry out, indirectly at least, the experiment 

 suggested by the old philosophers right up to the stage 

 when the second school is proved correct, and the 

 ultimate atom of lead reached. For convenience, we 

 will start with a standard decimetre cube of lead 

 weighing 11-37 kilograms, and the operation of section 

 will consist of three cuts at right angles to each other, 

 dividing the original cube into eight similar bodies 

 each of half the linear dimensions and one-eighth the 

 weight. Thus the first cube will have 5 cm. sides and 

 weigh 1-42 kilograms, the second will weigh 178 gm., 

 the fourth 2-78 gm., and so on. Diminution in the 



1 From an evening discourse delivered before the British Association at 

 Hull, September 12, 1922. 



no. 2769, vol. no] 



series is very rapid and the result of the ninth operation 

 is a quantity of lead just weighable on the ordinary 

 chemical balance. The results of further operations 

 are compared with suitable objects and a scale of 

 length in Figs. 1, 2, and 3. The last operation possible, 

 without breaking up the lead atom, is the twenty- 

 eighth. The twenty-sixth cube is illustrated in Fig. 3. 

 It contains 64 atoms, the size, distance apart, and 

 general arrangement of which can be represented with 

 considerable accuracy, thanks to the exact knowledge 

 derived from research on X-rays and specific heats. 

 On the same scale are represented the largest atom, 

 cresium, and the smallest atom, carbon, together with 

 molecules of oxygen and nitrogen, at their average 

 distance apart in the air, and the helical arrangement 

 of silicon and oxygen atoms in quartz crystals discovered 

 by X-ray analysis. The following table shows at what 

 stages certain analytical methods break down. The 

 great superiority of the microscope is a noteworthy 

 point. 



Just as any vivid notion of the size of the cubes 

 passes out of our power at about the twelfth — the 

 limiting size of a dark object visible to the unaided 

 eye — so when one considers the figures expressing the 

 number of atoms in any ordinary mass of material, 

 the mind is staggered by their immensity. Thus if 



Fig. 2. — Cubes 17 to 21 compared with minute objects to scale. 



we slice the original decimetre cube into square plates 

 one atom thick the area of these plates will total one 

 and one-quarter square miles. If we cut these plates 

 into strings of atoms spaced apart as they are in the 



