148 



SCIENCE 



[N. S. Vol. XXXVI. No. 918 



One would further gather the impression 

 that while the citrus industry of California 

 is beyond danger, that of Florida is liable to 

 be wiped out completely. While it is true 

 that the freeze of February, 1895, killed a 

 large part of the orange trees to the ground, 

 the few groves then existing in the southern 

 part of the state, where citrus planting is now 

 most active, largely escaped, and most of the 

 groves further north have long been in bear- 

 ing again. In other words the grower of 

 citrus has learned what Mr. Palmer has not 

 learned, i. e., that there is a difference in 

 climate between northern and southern Flor- 

 ida, and has accordingly shifted the center of 

 the industry a hundred miles further south. 

 He has further learned to copy the methods of 

 the California grower in being prepared to 

 heat his grove in case of need. 



As to the frost at Miami, the author knows 

 from personal observation that tomatoes were 

 not injured and every gardener knows that a 

 frost that will not kill tomatoes does not cut 

 much of a figure. Furthermore the tempera- 

 ture given for San Francisco and Los Angeles 

 (42) is perilously near the danger point for 

 frost, a fact that Mr. Palmer fails to mention. 



While every night may not be a " June " 

 night, in the writer's opinion our coldest 

 days, even in this part of the state, so far as 

 personal comfort is concerned, compare very 

 favorably with some " June " days he has ex- 

 perienced on the shores of Lakes Erie and 

 Michigan. 



One should not attempt to draw conclusions 

 as broad as his on such limited data. Figures 

 of minimum temperatures, although valuable, 

 fall a long way short of telling the whole 

 story as to the desirability of a state as a 

 winter resort. The average temperature dur- 

 ing daylight, for instance, is a point much 

 more important. 



I am impelled to write this protest because 

 of the amount of harm such an unjust article 

 can do to a community. 



J. E. Watson 



"University of Florida, 

 Gainesville 



SCIENTIFIC BOOKS 

 The Mechanics of the Aeroplane. A Study of 



the Principles of Flight. By Captain 



DucHENE. Translated by Ledeboer and 



Hubbard. Longmans, Green & Co. 1912. 



231 octavo pages, 81 diagrams, 4 tables in 



the text and 5 in the appendix. 



This is an elementary technical work on the 

 principles of the aeroplane. It is neither ac- 

 curate enough nor comprehensive enough to 

 be called a popular treatise. It presents in 

 rough and ready practical form the latest re- 

 sults of theory and experience, and therefore 

 should prove welcome to engineers who prac- 

 tise aviation professionally, rather than in- 

 vestigate profoundly or precisely. 



It is divided into four parts aggregating six 

 chapters. The first part treats of flight in 

 still air; the second part treats of equilibrium 

 of the aeroplane in still air; the third dis- 

 cusses the effect of the wind on the aeroplane ; 

 the fourth presents one chapter on the theory 

 and design of the screw propeller. In all the 

 text care is taken to preserve the theoretical 

 nature of the work, and not to cumber it with 

 descriptions of machines, details of construc- 

 tion, or historical references. 



The work would be improved by eliminating 

 certain misleading passages. Thus the au- 

 thor states that the wind force on a plane at 

 small angles of incidence is almost normal 

 to the surface, whereas it is well known that 

 the force may be very oblique at small angles, 

 being actually tangential to the surface at 

 zero incidence. Again he states that many 

 constructors design their propellers with a 

 curved leading edge because the streaky marks 

 on the propeller-blade made during rotation, 

 by dust particles and oil, assume this shape. 

 As the author presents without protest or 

 repudiation this absurd reason of the practical 

 designer, the reader naturally infers that the 

 author either endorses the absurdity or sus- 

 pends judgment. One skilled in aerodynamics 

 can not entertain such a reason for curving 

 the leading edge of a propeller blade. 



On the whole the book is a good presenta- 

 tion of the most advanced information on the 



