ii2 Presidential Address 



to discover negative parallaxes, or to prove that all par- 

 allaxes are higher than a certain limit, we should have a 

 choice between two conclusions : we could give up Euclid- 

 ean geometry, or modify the laws of optics, and suppose 

 that light is not rigorously propagated in a straight line. 

 It is needless to add that everyone would look upon this 

 solution as the more advantageous. Euclidean geometry, 

 therefore, has nothing to fear from fresh experiments. " 



Page 1 6 



By "Euclid's Postulate" is meant the famous postulate 

 or axiom above referred to. It is commonly called ' ' Axiom 

 12" in textbooks of Euclid elements. It lies at the base of 

 all his doctrine of parallels, and it leads direct to the con- 

 clusion that the three angles of a triangle are together 

 equal to two right angles. In fact it is another form of 

 stating that proposition. 



Page 17 



The "Preface" referred to is the Introduction by Sir 

 Joseph Larmor, M.P., Lucasian Professor of Mathematics 

 in the University of Cambridge, to the English translation 

 of Pomcare"'s book called Science and Hypothesis (Scott). 



Page 28 



Boyle's Law is that the volume of a gas varies inversely 

 with the pressure to which it is subjected. It is a natural 

 consequence of the kinetic theory of gases in its simplest 

 form; but, when considered strictly, it is seen to involve 

 the assumption that the gaseous particles are infinitely 

 small so small that they can never become the least 

 crowded, however great the pressure, and further that 

 there is no attractive force or incipient cohesion acting 



