A Description of a new Military Bridge. 347 



copied it into their works in its original inaccurate state. It 

 should be — To log. secant latitude, add log. cosecant hor. angle 

 and log. change of declination ; the sum will be be the log. of 

 correction of azimuth, &c. 



I may perhaps give the investigation afterwards. We can 

 never be too much on our guard against error. 

 I am, sir, 



Your most obedient servant, 

 Berners-street, Nov. 2, 1819. HenRY MeikLE. 



P. S. — Mr. Tredgold has by no means refuted my objections; 

 but I cannot now attend to his case. 



LIX. A Description of a new Military Bridge, that may he 

 made of short Pieces ofTimler, and easily put together in 

 any Situation. The same Method is applicable to other Uses. 

 By A Correspondent. 



To Mr. Tilloch. 



Sir, — X HAVE called the combination of timbers now to be 

 described a military bridge, not because it is peculiarly adapted 

 to that purpose, and that purpose only, for it is equally applica- 

 ble to any other portable bridge, or other erection of a temporary 

 nature, but because as a military bridge it would be most useful; 

 and whoever considers the difficulty which the passage of a river 

 or canal son'jetimes offers to an army, will allow me, without cen- 

 sure, to offer a hint that may be of use on such an occasion. 



There are some who will object to the introduction of such a 

 subject at the present time : to these it will only be necessary to 

 state, that the education of engineers must not be neglected, even 

 in peaceful times, unless indeed we should intend to become an 

 easy prey to some other nation, or to call in the assistance of a 

 more warlike race. Britain, I hope, will never be reduced to auch 

 a state, through the neglect of cultivating those sciences and habits 

 which constitute the strength of nations. 



Lately, the construction of military bridges has beeu very ably 

 treated in an Essay by Col. Sir H. Douglas, who has in that work 

 described a simple combination of much merit, which may be 

 extended to a 2(j feet span *, In order to span either a .'iO feet 

 opening, or any smaller one, I offer the following method. 



Let two or more frames be put together, as is shown by the sketcii 

 in 348. When these frames arc placed across a river, or other 

 opening, with cross-bearers notched upon them, and planks for 



• Essay on tlie Construction of Military Bridges, ;>. \M. 



a road- 



