August 19, 1909J 



NATURE 



21 



But he has, at all events, laid those who are inter- 

 ested in cytological development under a debt of 

 gratitude by the exhaustive treatment he has accorded 

 to those topics which he decided to discuss. 



MARINE PROPELLERS. 



The Screw Propeller: and other Competing Instru- 

 ments for Marine Propulsion. By A. E. Seaton. 

 Pp. xii + 255. (London : Charles Griffin and Co., 

 Ltd., igog.) Price 12s. 6d. net. 



THE author of this book is well known, both as \ 

 a practising marine engineer and as an autlior. 

 His " Manual of Marine Engineering " has long 

 served as a text-book, and has passed througii many 

 editions. It was natural, therefore, that the an- 

 nouncement of a work by Mr. Seaton dealing with 

 marine propellers should awaken interest over a 

 wide circle of readers, more especially as the problem 

 of propeller design has not yet received a complete 

 solution. .'Vs Mr. Seaton says, "even in modern 

 times .... our best men do sometimes fail to 

 achieve success," although there are now available 

 the results of much experimental and theoretical in- 

 vestigation on the subject, .^fter seventy years' con- 

 tinuous work it still remains true that when novel 

 types of ships or unprecedented speeds have to be 

 attempted, although use may have been made of all 

 available data, and the best advice taken, full success 

 is not alwa3's or at once achieved. On the contrary, 

 considerable gains in efficiency are frequently attained 

 by a process of " trial and error," out of which comes 

 a final selection of the propeller forms and dimensions 

 best suited to novel conditions. 



Such a confession may be thought discreditable; 

 indeed, it is sometimes so treated by critics who 

 have not themselves had occasion to undertake re- 

 sponsibility for ship and propeller designs ; but it 

 represents the facts of the case, and the explanation 

 is not far to seek. When a problem has been unsuc- 

 cessfully attacked by men like Rankine and William 

 Froude, amongst those who have finished their work, 

 and by men like R. E. Froude, Cotterill, Greenhill, 

 and D. W. Taylor, who are still alive and interested 

 in finding solutions, it may be presumed that the 

 problem involves considerable difficulties. When one 

 considers the almost endless variety of the conditions 

 involved in ship propulsion, the failure to reach a 

 complete solution of the problem need not cause as- 

 tonishment, and it is reasonable to anticipate that we 

 shall have to be content for some time to come, if not 

 permanently, with partial solutions chiefly based on 

 experimental investigations, and on careful scientific 

 analyses of the results. 



Mr. Seaton definitely states in his preface that the 



" object of the present work is to amplify and extend 

 what [had been g'iven] in skeleton or in rudimentary 

 form " (in his " Manual of Marine Engineering ") in 

 the shape of rules for guidance in the practical work 

 of designing propellers. These rules are said to have 

 been " generally based on scientific reasons and 

 always capable of giving results agreeable with the 

 best and most successful practice " : and it is claimed 

 that by means of successive improvements " they 



NO. 2077, VOL. Si] 



have become generally applicable to the design of a 

 screw for an ."Atlantic liner or a torpedo boat." It 

 is added that " the more abstruse and highly mathe- 

 matical investigations connected with the theory of 

 the resistance of ships and propellers have been left 

 to be studied in the text-books and .... valuable 

 papers " of various authors. 



More or less empirical rules such as Mr. Seaton 

 proposes no doubt have a certain value as representing 

 his own practice and deductions from his study of 

 published results of steamship trials, but it cannot be 

 admitted that such rules can be depended upon abso- 

 lutely when new conditions have to be faced. If it 

 were true that the best results could be ensured by 

 the use of any known rules in the designs of screws 

 over the wide range from " an .Atlantic liner to a 

 torpedo boat," difficulties such as have been mentioned 

 ivould disappear, and the work of the naval architect 

 would become easy of performance. The occurrence 

 of these difficulties demonstrates the imperfection of 

 existing rules. 



Turning to the general scheme of the book, it may 

 be said that the section dealing with the history of 

 marine propellers is both interesting and valuable. 

 Bourne's book, giving the early history of the screw 

 propeller, is not now generally accessible, and Mr. 

 Seaton's summary will be found useful for reference. 

 Paddle wheels, screws, and hydraulic (or jet) pro- 

 pellers are treated separately, their principles of action 

 are explained, rules being given for their practical 

 design. One chapter is devoted to an explanation, in 

 popular language, of the modern theory of the re- 

 sistance of water to the motion of ships, but readers 

 desiring full information on the subject will neces- 

 sarily have to turn to other sources, as Mr. Seaton 

 only attempts a brief sketch. Naturally, screw pro- 

 pellers claim most attention, their various forms, 

 numbers and positions are described ; and the effects 

 of changes in numbers, shape, and proportions of 

 blades are also discussed at some length. Much 

 information has been collected and collated re- 

 specting experimental trials made with screw pro- 

 pellers, but it seems doubtful whether the large 

 amount of space devoted to trials made by the Ad- 

 miralty and other experimentalists in the early period 

 of screw propulsion might not have been better 

 utilised, seeing that these trials were made on ships 

 the forms, proportions, and speeds of which in no 

 way represent present practice, while many important 

 conditions affecting results are not definitely known. 

 An antiquarian interest attaches to them, and 

 from their consideration certain useful deduc- 

 tions may be, and, indeed, have been, made; 

 but radical differences exist between conditions 

 prevailing thirty or forty years ago and those 

 of the present day, and the devotion of much time to 

 this subject, when better and later information is 

 available, is not desirable. The chapters dealing with 

 the geometry of the screw and materials used in the 

 construction of the screw propeller are excellent. 



The book is well produced and illustrated. It has 

 an excellent index, and as a work of reference will be 

 found of service to all interested in the propulsion 

 of ships. 



