288 Major-General Sir Howard Douglas on 



be all carefully studied, their respeclive merits well considered, 

 and their applications most minutely scrutinized, by those pro- 

 fessionally engaged in their construction. 



Besides a knowledge of the scientific principles on which 

 bridges are constructed, an acquaintance with the general laws 

 observed by fluids in motion is of much practical advantage to 

 the civil and military engineer. By a proper application of these 

 laws, the most advantageous position for a bridge may be select- 

 ed, and its permanence secured. On this account Sir Howard 

 Douglas commences his work properly with a section on the 

 principles and effects of the motion of water in rivers. He justly 

 remarks : 



" Although it is not the object of this work, to consider the doctrine of the 

 motion of water in canals and rivers, in relation to the purposes of civil life, 

 yet so many deductions, highly important to our present subject, may be 

 made from it, that a few observations upon hydraulics will be found a useful 

 introduction to the various methods of passing rivers in military operations. 



" A knowledge of the principles of the motion and action of water, enables 

 us to trace that mode of unceasing operation which occasions sinuosities ; re- 

 gulates the velocity of the current ; forms eddies, and consequently banks ; 

 determines the natures of the sections at different parts of rivers, and many 

 other points connected with their local circumstances, essential to the proper 

 application, construction, and security of military bridges, and to the calcula- 

 tion of the effects or the delivery of water, whether for inundation, subsist- 

 ence, or force." — Pages 1 and 2. 



Sir Howard Douglas then notices the imperfect theories of 

 Guglielmini and Varignon. The latter became proverbial among 

 the academicians at Paris, for a predilection to generalizations, 

 without a sufficiently careful appeal to experiments ; and even 

 Belidor, who has been considered one of the most profound of 

 scientific engineers, adopts the same theories in his ArcJiitccture 

 Hydraullque. The applications of these theories, however, to 

 the courses of the rivers Po and the Danube, showed their im- 

 perfections ; and the Abbe Bossut and the Chevalier Du Buat 

 were by tjiat means induced to undertake each, an extensive 

 and varied series of experiments in hydrodynamics, for the ex- 

 press purpose of improving these theories. The former was 

 himself an eminent mathematician, and applied his extensive 

 knowledge of that science very successfully to the subject. The 

 latter was assisted by a talented young officer of engineers, M. 

 Benzech de St Honore, who had been appointed his colleague 



