_Sixty-sixth Lecture._--(10.) Object, disposition, and armament of all the batteries from the first opening of the trenches to the capture of the place. Use of field artillery to flank the batteries, &c. Service of artillery in the defense of the place. Supply of ordnance, projectiles, powder, small-arms, and different carriages. Personnel of the artillery. Troops, staff. Organization of the personnel and of the duties by local divisions. Precautionary armament; supply of ordnance. Defensive armament. Armament of the different works. Service of the pieces. Last defensive armament. _Lectures Preparatory to the Labors of the Course._ 1. Drawing and tracing of ordnance, 3 lessons. 2. Design for ordnance, 4 “ 3. Application of the theories of the course, 1 “ 4. Drawing of artillery material, 1 “ 5. Tracing of batteries, 1 “ The sixth lecture of the fourth part of the course (the fifty-sixth) is partly devoted to the communication of the instructions necessary for the execution of the work of tracing plans of batteries. _Studies in connection with the Artillery Course._ The practical studies which are connected with the artillery course, are,-- 1. Drawing of ordnance, 12 days. 2. The designs for ordnance, 24 “ 3. The application of the theories of the artillery course, 6 “ 4. The drawings of artillery material, 26 “ 5. The tracing of batteries, 4 “ -- Total, 72 days. The tracing of batteries is executed by the students of both arms, the other tasks by the artillery students alone. I. DRAWING ORDNANCE (12 DAYS.) The survey of ordnance consists in constructing accurate sketches of a gun, howitzer, and mortar, in measuring their dimensions, and in giving a description of each of the pieces drawn. It is on this occasion that the students are practiced in the management of instruments to insure precision, such as the _étoile mobile_, and the sliding compass, &c. One day is devoted to this work. The tracing of ordnance consists in the execution of a drawing upon colombier paper, containing an exact and detailed representation of a gun, a howitzer, and a mortar, with their projectiles. This work is performed with the help of the tables for the construction of ordnance. Eleven days are devoted to it. _Detailed Programme of the Drawing._ 1. For each gun, howitzer, or mortar, a longitudinal section in the direction of the axis, and at right angles to the axis of the trunnions, and a plan parallel to the axis of the bore and of the trunnions.