L. MECHANICS AND ENGINEERING. 455 



large quantity of ammunition maybe wasted without the effect 

 being observable from the battery, and points to the necessity 

 of some means being provided for ascertaining in the field, 

 and within reasonable limits, the distance of the object to 

 be lired at. Captain Nolan's apparatus is fitted to two of 

 the guns of a battery, and enables the distance of the object 

 to be determined with sufficient accuracy after firing two or 

 three rounds. Min. of Hoy. Artillery Institution ^ WW. ^ 161. 



SHARP ARTILLERY PRACTICE. 



At the siege of Strasburg the Prussians used for breach- 

 ing purposes a short six-inch gun firing a special long shell 

 weighing about sixty pounds. The method of breaching 

 consisted in makincj a horizontal cut at a height from the 

 bottom equal to one third of that of the wall; and when this 

 cut was supposed to be satisfactorily eflfected, vertical cuts, 

 if necessary, were made, the continued firing eventually bring- 

 ing down the wall. The fact that the horizontal cut was 

 satisfactorily completed could generally be decided by the 

 sound of the concussion and explosion of the shell, by the 

 nature of the fragments whirled into the air, and by the ap- 

 pearance of the smoke from the explosion of the projectile, 

 it being, if delayed, of a dark-gray color, and slow in rising 

 if the masonry had been broken through. One of the chief 

 sources of strensrth of the fortress of Strasburo: consists in 

 the obstacles presented by difiTerent water ditches, and by the 

 extensive inundations which can be formed in its vicinity. 

 The French, by damming up the 111 and utilizing the sluices, 

 had filled not only the ditches and the whole country oppo- 

 site the south front, but had inundated a great part of the 

 ground of the left flank of the attack. The plans of the fort- 

 ress showed the besiegers that by the destruction of two 

 particular sluices, the water upon the ground and in the 

 ditches would be reduced to a very low level; but neither of 

 the sluices could be seen from any part of the attacking lines. 

 Neither did the inaccurate maps afford sufficient data by 

 which to point the guns. It was known that the sluice was 

 near a turret, and a certain turret was fired upon, until, by 

 the firing, its exact distance was determined. Plotting this 

 upon the chart, it was then found that this could not be in 

 the neighborhood of the sluice. A second turret was fixed 



