ILLUSTRATIONS 



A SAND-STORM ON THE MOJAVE DESERT Facing p. 2O2 



BENJAMIN THOMPSON (COUNT RUMFORD) " 208 



THOMAS YOUNG " 2l8 



MICHAEL FARADAY " 228 



SIR HUMPHRY DAVY " 234 



HERMANN LUDWIG FERDINAND HELMHOLTZ .... " 252 

 JAMES PRESCOTT JOULE .... 



WILLIAM THOMPSON (LORD KELVIN) 



270 

 JULIUS ROBERT MAYER 



JOHN TYNDALL . . . 



