NOTICES OF NEW BOOKS. 319 
theories and conclusions based on marine animal life. Dr. Hjort 
soon puts the discussion on a sound foundation. We read :— 
** But no definite human idea of the fitness of adaptations is of 
any value as knowledge. No more does any human idea neces- 
sarily correspond to the reality occurring in nature. The idea 
is only valuable as stimulating the investigator to seek realities. 
And reality in the scientific sense means a definite, positive 
mechanism, existing in the organism itself or in the surrounding 
medium. The object of investigation is to understand these 
mechanisms ; the leading idea may often prove an empty fancy 
beyond the world of realities.” 
As regards the ‘‘ Colours of Marine Animals,” much informa- 
tion and cautious discussion, assisted by beautiful illustration, 
are supplied. Here Dr. Hjort is again candid and just. He 
writes :—‘‘ From time immemorial seafaring men have possessed 
a certain amount of knowledge as to the colours of marine 
animals. Sailors know well the sky-blue colours peculiar to the 
tropical surface forms. MHerring-fishermen also know that the 
blackish-brown back of the herring is almost invisible from 
above, and only when occupying a slanting position or making a 
sudden turn does the herring become visible, its mirror-like sides 
emitting a silvery flash. The deep-sea fishermen are equally 
acquainted with the dark, black, brown, violet, or red colours 
peculiar to deep-sea animals. No scientist can claim the dis- 
covery of these phenomena, which are as well known as the 
colours of the ocean itself.” 
This volume contains excellent portraits of those well-known 
authorities who have made Oceanography a science. 

Science of the Sea. An Elementary Handbook of Practical 
~ Oceanography for Travellers, Sailors, and Yachtsmen. Pre- 
pared by The ‘Challenger’ Society. Edited by G. Harpert 
Fow.er, B.A., Ph.D., &c. John Murray. 
Ovr previous notice referred to the work done in Oceano- 
graphy by special and experienced scientists ; the present volume 
is intended for the use of volunteers in the same field of observa- 
tion. We prefer the term “scientific volunteer” to that of 
‘‘amateur,”’ the latter name being frequently a term expressive 
