38 W. Thompson on the size of Atoms. 
many of these granules show distinct cleavages, which exhibit 
a hexagonal outline. Searching the ground carefully I found 
wormlike contorted he A in shape like the similar forms of 
some chloritic minerals. substance is distinguished from 
quartz by its low specific sanity =1°961, and inferior hardness 
(near 6). It is mostly soluble in caustic potash, leaving only 
per cent insoluble, which seemed to consist, in part at least, of 
the original m ineral. On ignition it loses 7-27 per cent water. 
It is therofes 4 manifestly amorphous quartz or opal. Indeed 
small masses of ae opal of various colors are found 
in the neighborhoo 
It hence appears, that micaceous structure is not, as is fre- 
quently assumed, the absolute closing scene of the metamor- 
phism of minerals, but that the replacing power of silica is able 
to overcome the antimetamorphic energies of minerals even, 
which have arrived at the micaceous stage. 
Bethlehem, April 22, 1870. 
Art. VL—On the Size of Atoms; by Prof. Sir W. THomson, 
: F.RS* 
THE idea of an atom has been so constantly associated with 
incredible assumptions of infinite strength, absolute rigidity, 
mystical actions at a distance, and indivisibility, that chemists 
and many other reasonable naturalists of modern times, losing 
all patience with it, have dismissed it to the realms of metaphys- 
ics, and made it smaller than “ anything we can conceive.” 
But if atoms es inconceivably small, why are not all chemical 
actions infinitely swift? Chemistry is powerless to deal with 
this Setar and many others of paramount importance, if 
ba ardness of its fundamental assumptions, from 
Ssntempiating the atom as a real portion of matter occupying 
a finite space, and forming a not immeasurably small constitu- 
ent of any palpable body. 
. More than thirty years ago naturalists were scared by a wild 
ge ea of Cauchy’s, that the familiar Linder aye colors 
proved the “sphere of sensible molecular acti in trans- 
Se tea ree and solids to be comparable wills ‘the wave- 
: The thirty years which have intervened have 
poe Sinat that proposition. They have produced a large 
number of capable judges; and it is only ineapen to judge 
in dynamical questions that can admit a doubt of the substan- 
tial correctness of Cauchy’s conclusion. But the “sphere % 
molecular action” conveys no very clear idea to the non-mathe- 2 
* From Nature, No. 22, March 31. 
aii 
