118 
Proceedings of the Royal Society 
Monday, 1 §th March 1885. 
THOMAS STEVENS OH, Esq., Memb. Inst. C.E., President, 
in the Chair. 
The following Communications were read 
1. Hooke’s Anticipation of the Kinetic Theory and of 
Synchronism. By Professor Tait. 
{Abstract.) 
While collecting materials for a Text-book of the Properties of 
Matter , the author had occasion to consult the very curious pamphlet 
by Robert Hooke, entitled Lectures de Potentia Reditutiva , or of 
Spring (London, 1678). In this work there is a clear statement of 
the principle of Synchronism, which was applied by Stokes to the 
explanation of the basis of Spectrum Analysis. There is also a very 
remarkable statement of the elementary principles of the modern 
Kinetic Theory of Gases, the first mention of which is usually fixed 
sixty years later, and ascribed to D. Bernoulli in his Hydrod.ynamica 
(Argentorati, 1738). 
2. On the Hexagonal System in Crystallography. By 
Professor Crum Brown. 
The forms of the uniaxial systems may be regarded as derived 
from forms, or parts of forms or combinations, of the regular system 
by uniform expansion or contraction in a direction parallel to the 
axis of the uniaxial system, i,e ., normal to a face of the cube for the 
tetragonal, and normal to a face of the octahedron for the hexagonal 
system. Faces, therefore, which are, in the regular form or com- 
bination, at right angles to or parallel to such axis, retain their 
relative angular position unchanged in the uniaxial form or combina- 
tion, and can be represented by means of indices referring to the 
rectangular axes of the regular system, whatever be the amount of 
the deformation (expansion or contraction). These faces are prism 
faces, parallel to the axis, and basal faces at right angles to it, All 
other faces have their angular position affected by the deformation. 
