MECHANICS AND USEFUL ARTS. 117 



possible to reach the solid ground with cast-iron tubes sunk with 

 compressed air, or with any other system ; but neither the imple- 

 ments nor the suitable workmen were available in the colony, — 

 and it was a great expense to bring them, and especially the 

 workmen, from France. The use of timber piling was, of course, 

 out of question, as timber is very expensive in Algiers and 

 quickly becomes rotten ; but there was a set of boring implements 

 with which the men used to work it. The engineers began bor- 

 ing holes 10 inches diameter down to the solid ground. These 

 holes, lined with thin plate-iron pipes, were afterward filled with 

 concrete up to the very level of the ground. Each of these con- 

 crete columns bears a cast-iron column ; these columns are prop- 

 erly braced together, and support the girders of the viaduct, which 

 is divided into spans of about 20 feet, and is 20 feet high over 

 the ground. This system has succeeded very well, and is to be 

 extended to another larger valley. — Van Nostrand''s Eclectic 

 Engineering Magazine^ Sept., 1869. 



EXPERIMENTS ON HEAVY ORDNANCE. 



The following conclusions, deduced from experiments on heavy 

 ordnance, are given in the Report of the Ordnance Committee, 

 presented to the Senate, February 15, 1869 : — 



1. That no more heavy guns should be purchased for mounting 

 in the fortifications or use on shipboard until such improvements 

 are made in methods of fabrication as will insure more reliable 

 endurance than has heretofore been exhibited. 



2. That the Rodman system of gun-making, while partially 

 successful in smooth bores and small calibres, has so far failed in 

 rifles of large calibre as to show it to be unworthy of fiu'ther 

 confidence. Recent improvements in defensive works and armor- 

 IDlutiug render heavy rifled guns the most efficient means of 

 attack, and no system of fabrication which does not furnish such 

 guns should be adopted or continued. The principle of initial 

 tension, which is the basis of the Rodman system, appears to be 

 of doubtful utility, as applied by General Rodman, especially for 

 rifled guns. This tension, it is admitted, gradually disappears 

 from the gun witii age, and in time is entirely lost. 



3. That guns cast solid, in the manner practised in the navy 

 under the tlirection of Rear-Admiral Dahlgren, while exhibiting 

 satisfactory endurance as smooth bores with small charges and 

 hollow projectiles, have not the requisite strength for rifles of 

 large calibre. This mode of casting seems to be defective in 

 principle, as the tensions inaugurated in cooling have a tendenc}'' 

 to aid the powder to rupture the gun. 



4. That experiments should be at once conducted for the pur- 

 pose of ascertaining the real cause of the bursting of heavy 

 guns, and of determining upon some method of fabrication that 

 will secure uniform endurance. 



5. That every encouragement should be given to inventors, 



