SCIENCE 



A WEEKLY JOURNAL DEVOTEE TO THE ADVANCEMENT OF SCIENCE, PUBLISHING THE 



OFFICIAL NOTICES AND PROCEEDINGS OF THE AMERICAN ASSOCIATION 



FOR THE ADVANCEMENT OF SCIENCE . 



Friday, March 29, 1907 



CONTENTS 

 The Factors of Safety in Animal Structure 

 and Animal Economy: De. S. J. Meltzee. . 481 



Scientific Books: — 



Some Recent Bibliographies of Geology: 

 De. F. H. Bain. Lowell on Mars and its 

 Canals : Dr. Herman S. Davis 498 



Societies and Academies: — 



The Torrey Botanical Cluh : Dr. C. Stuaet 

 Gagee 500 



Special Articles: — 



The Limitations of Isolation in the Origin 

 of Species: Professor Charles Atwood 

 KoFOiD. 'Sote on a Tertiary Basin in 

 Northern Alaska: E. M. Kindle 500 



Quotations : — 



The University of Maine 507 



•Current Notes on Land Forms: — 



Drainage Changes in California: D. W. J. 

 The Peneplain of Brittany: W. M. D. 

 Physiographic Types: W. M. D. System- 

 atic Physiography : W. M. D 508 



■The New Geological Survey of Bramil: Peo- 

 FESSOB J. C. Branner 510 



The FayUm Eaipedition of the American Mu- 

 seum: H. P. 513 



Scientific Notes and News 516 



University and Educational News 520 



MSS. intended for publication and boots, etc.. Intended fot 

 re-riew siiould be sent to the Editor of Science, Garriaon-on- 

 Hudson, N. Y. 



TEE FACTORS OF SAFETY IN ANIMAL 

 STRUCTURE AND ANIMAL ECONOMY'- 



The living animal body is like a machine 

 in action. Like a machine its structures 

 are subject to a variety of stresses, and 

 like a machine the work is accomplished by 

 an expenditure of energy derived from a 

 supply of fuel. I intend to discuss in this 

 lecture, vrhether, as in the human-made 

 machines, the structures and functions of 

 the animal mechanism are provided with 

 factors of safety. The term 'factor of 

 safety' is employed in engineering to desig- 

 nate the margin of safety required in the 

 building of engines, bridges, houses, etc. 

 For instance, in designing a boiler, if the 

 tensile strength of the steel of which the 

 plates and stay-bolts are made, is 60,000 

 pounds per square inch, the actual stress 

 which is allowed for the work of the boiler 

 should not be more than 10,000 pounds per 

 square inch for the plate and not more 

 than 6,000 pounds per square inch for the 

 stay-bolts; that means the stress to which 

 the plates or the bolts may be exposed in 

 the boiler should only be one sixth or one 

 tenth of the actual strength of the steel. 

 The factors of safety are said to be here 

 six for the plate and ten for the bolts. In 

 some instances the required factors of 

 safety may be as low as three, in other cases 

 again they may be as high as twenty and 

 even forty. The character of the stress to 

 which the structures might be subjected is 

 an important point in deciding upon the 



'Harvey Society lecture, delivered at tlie New 

 York Academy of Medicine, December 15, 1906. 



