CONTENTS 



I 



PAGE 



ON A PIECE OF CHALK [1868] 1 



(A Lecture delivered to the working men of 

 Norwich during the meeting of the British 

 Association.) 



II 



THE PROBLEMS OF THE DEEP SEA [1873] 37 



III 



on rome of the "results of the expedition of h.m.s, 



•'challenger" [1875] 69 



IV 



YEAST [1871] 110 



