Structure of the Universe 405 



played a most important role. It is the most universal agent known. 

 And, notwithstanding all this does it not seem strange that its cause 

 has remained unknown until now? Yet, this need not surprise us; 

 for the predominant characteristic of man is, and has always been 

 his ignorance of the things concerning himself and nature around him. 

 Taking the history of mankind as extending over several thousand 

 years at least, we may say that it was only yesterday that he learned 

 that his blood circulated in his body, that the atmosphere had weight, 

 and that the earth went round the sun. With the liberation of man's 

 mind through the aid of science he is now beginning to realize some- 

 thing of his own possibilities, and to cast a prophetic eye towards the 

 future, which holds within its womb possibilities for him yet un- 

 dreamed of, as the fruit of his knowledge. Man's mind is not yet 

 exhausted. It is only beginning its career of conquest over nature. 



Dr. Carl Barus in his "Progress of Physics in the Nineteenth Cen- 

 tury" remarks: "Just as the 19th century began with dynamics and 

 closed with electricity, so the 20th century begins anew with dynamics 

 to reach a goal, the magnitude of which the human mind can only 

 await with awe." 



March 8, 1910. 



List of tne Steps Which Led Reynolds to the Discovery of Gravitation. 



1. On the Extent and Action of the Heating Surface of Steam Boil- 

 ers. Pages 81-85, Vol. I. Papers on Mechanical and Physical 

 Subjects. 1874-5. 



2. On Certain Dimensional Properties of Matter in the Gaseous State. 

 Pages 257-390. Vol. I., Papers on Mechanical and Physical Sub- 

 jects. 1879. 



3. On the Equations of Motion and the Boundary Conditions for Vis- 

 cous Fluids. Pages 132-137. Vol. II., Papers on Mechanical and 

 Physical Subjects. 1883. 



4. Experiments showing Dilatancy, a Property of Granular Material, 

 possibly conected with Gravitation. Pages 217-227, Vol. II., Pa- 

 pers on Mechanical and Physical Subjects. 1886. 



On the Dilatancy of Media Composed of Rigid Particles in Contact. 

 With Experimental Illustrations. Pages 203-216. Vol. II., as 

 above. 1885. 



5. On the Dynamical Theory of Incompressible Viscous Fluids and 

 the Determination of the Criterion. Pages 585-577, Vol. II. 

 Papers on Mechanical and Physical Subjects. 1895. 



— Cambridge University Press, London. 



Relation of Full Space to Empty Space in Different Piling^ of Round 



Particles. 



Space of Full Empty 



Volume. Space. Space. 



1. Vertical Position 100 52.381 47.619 



2. First Triangular Position 100 59.864 40.136 



3. Second " " 100 69.841 30.159 



4. Third " " 100 79.818 20.182 



5. Fixed Pyramidal " 100 72.877 27.123 



6 Fixed Quadrilateral " 100 74.830 25.170 



