AMERICAN JOURNAL OF PHYSICS VOLUME 16, NUMBER MAY, 1948 

NOTES AND DISCUSSION 

Franklin's Discovery of the Electron 
ROBERT A. MILLIKAN 

California Institute of Technology, Pasadena 4, California 

I N celebrating the anniversary of the discovery of the electron, it is a mistake to concentrate attention solely 
on J. J. Thomson's paper of 1897. I do not in any way 
underestimate the importance of that paper in bringing 
about general acceptance of the electron theory of matter, 
through the evidence presented in it for the existence of a 
charged particle of mass about 1/1000 the mass of the 
hydrogen atom. However, to this particle Thomson gave 
the name ''corpuscle," rather than electron, doubtless 
because the word "electron" had already been assigned by 
G. Johnstone Stoney to the hypothetical atom of electricity, 
that is, of electric charge, whether that charge is positive or 
negative. The existence of this atom of charge, or of the 
atomic constitution of electricity, was asserted with great 
clarity by Benjamin Franklin because of experiments 
begun in 1747, so that 1947 is both the 200th anniversary 
of Benjamin Franklin's discovery of the existence of an 
a tom of electric charge and the 50th anniversary of J. J. 
Thomson's proof of the existence of a charged particle 
whose mass, as he then phrased it, was about 1/1000 that 
of the hydrogen atom. 

These two conceptions have unfortunately been con-
fused in much modern writing, though Thomson was 
careful to use the word "electron" in its original sense as 
an atom of charge, not of mass, and to call cathode rays a 
stream of "corpuscles." The most authoritative writers 
have continued to use the term "electron" to mean an 
element of charge, as G. Johnstone Stoney first defined it 
in publications in 1874, 1881 and in 1891.1 

How unambiguously Franklin conceived his theory of 
electricity and described the most important properties of 
the electrical atom is shown by the following quotation 
from his letter to Peter Collinson in his book published 
in 1774.2 

1. The electrical matter consists of particles ex-
tremely subtile, since it can permeate common matter, 
even the densest metals, with such ease and freedom as 
not to receive any perceptible resistance. 

2. If any one should doubt whether the electrical 
matter passes through the substance of bodies, or only 
over and along their surfaces, a shock from an elec-
trified large glass jar, taken through his own body, 
will probably convince him. 

3. Electrical matter differs from common matter in 
this, that the parts of the latter mutually attract, 
those of the former mutually repel each other. Hence 
the appearing divergency in a stream of electrified 
effluvia. 

4. But though the particles of electrical matter do 
repel each other, they are strongly attracted by all 
other matter. 

5. From these three things, the extreme subtilty 
of the electrical matter, the mutual repulsion of its 
parts, and the strong attraction between them and 
other matter, arise[s] this effect, that, when a quantity 
of electrical matter is applied to a mass of common 
matter, of any bigness or length, within our observa-
tion (which hath not already got its quantity) it is 
immediately and equally diffused through the whole. 

6. Thus common matter is a kind of spunge to the 
electrical fluid. And as a spunge would receive no 
water if the parts of water were not smaller than the 
pores of the spunge; and even then but slowly, if there 
were not a mutual attraction between those parts and 
the parts of the spunge; and would still imbibe it 
faster, if the mutual attraction among the parts of 
the water did not impede, some force being required 
to separate them; and fastest, if, instead of attraction, 
there were a mutual repulsion among those parts, 
which would act in conjunction with the attraction of 
the spunge. So is the case between the electrical and 
common matter. 

7. But in common matter there is (generally) as 
much of the electrical as it will contain within its 
substance. If more is added, it lies without upon the 
surface, and forms what we call an electrical atmos-
phere, and then the body is said to be electrified. 

I think the foregoing quotation clearly establishes the 
right of Benjamin Franklin to be considered the discoverer 
of the atom of electricity. The world has recently and properly 
celebrated the year 1947 as both the ZOOth anniversary of 
Franklin's discovery of the electron and the 50th anniversary 
of J. J. Thomson's unambiguous establishment of the electron 
theory of matter. 

1 See also R. A. Millikan, Electrons ( + and - ), protons, photons, 
neutrons, mesotrons and cosmic rays (Univ. of Chicago Press, 1947), 
pp. 332-333. 

2 Experiments and observations on electricity, made at Philadelphia in 
America, by Benjamin Franklin, L.L.D. and F.R.S. Member of the Royal 
Academy of Sciences at Paris, of the Royal Society at Giittingen, and of the 
Batavian Society in Holland, and President of the Philosophical Society 
at Philadelphia. To which are added, letters and papers on Philosophical 
subjects. The whole corrected, methodized, improved, and now collected 
into one volume, and illustrated with copper plates. (London, ed. 5, 1774), 
p. 54. The qnotation may also be found in I. B. Cohen's edition (Har-
vard Univ. Press, 1941), p. 13. 

A Convenient Viscosity Apparatus 
G. P. BREWINGTON 

Lawrence Institute of Technology, Detroit 3, Michigan 

T HE apparatus described herein has been found to be quite satisfactory for sophomore students and is 
sufficiently sensitive to indicate a change in the viscosity of 

319