OF PROJECTILES. l6ts

As st book of artillery, have been found adequate to everypurpose; nor can their surface be more polished, ortheir figures more perfect, without incurring an exor-bitant and unnecessary expence.

144. The initial velocities of (hot are determined fromexperiments made with (kill and discernment and conductedwith care and circumspection : before we proceed to the me-thod of determining them, it will be necessary to mentionthe principles adhered to in carrying on the experiments.

1. The piece was always loaded in the fame manner,and placed exactly in the fame position, lest the resultmight be erroneous.

2. Since effects are always proportioned to theircauses, when any remarkable differencearifes in the courseof the experiment, it should excite no amazement;as it must proceed from negligence or accident. Some •practitioners take the mean result of all experiments,but conclusions drawn from thence must be faulty.

3. In spite of the utmost precaution, there will besometimes a slight difference, proceeding from ihe man-ner of placing or wadding the powder, &c.

if the variations be not very great, a few more roundsmay be fired; but the mean result only of those takenthat approach nearest to each other : this may then be ■considered as the ablolute result. If, for example, thequestion be concerning the length of ranges ; the meanonly of those should be taken, whose differences do notexceed 2 in the 100, and no regard paid to the others;But, lhould the ranges vary considerably, it will thenbe necessary to examine carefully every part of theprocess, to discover the cause of the variations, and be.enabled to make fresh experiments in a more exactmanner.

J 45 - There are three methods of determining the initialvelocity of (hot:

1. By measuring their penetrations into a homoge-neous butt of a known consistency.

2. By analysing and resolving into its simple move-ments, the curve described by the projectile on quittingthe piece.

3. By deducing it from the thickness of metal of thefire-arm, when it is in equilibrio with the pressures of -the elastic fluid, in every point of its length, The

L 3 third