68 ANNUAL OF SCIENTIFIC DISCOVERY. 



flannel ba^s in which the ordinary charges for artillery are contained 

 are the chief causes of the fouling of the gun, the use of uncovered 

 solid cartridges obviously presents great advantages. Such cartridges 

 may be further rendered water-proof by coating them with a solution 

 of collodion. 



MECHANICAL PROPERTIES OF PROJECTILES. 



In a paper on the above subject presented to the British Associa- 

 tion, 1862, by Mr. W. Fairbairn, the author commenced by stating 

 that in the investigations which had taken place with regard to pro- 

 jectiles and armor-plated ships, one great difficulty that had arisen 

 was to get plates of sufficient thickness, and vessels of sufficient ton- 

 nage to carry those plates. It appeared that they were limited to 

 plates of five inches in thickness; with plates heavier than that a 

 ship would not be what was technically called "lively." He had 

 attended the experiments instituted by the government at Shoebury- 

 ness from the commencement, and they had reference to the force of 

 impact. He would state the results. The first series of experiments 

 had reference to the quality of the plates and the properties of the 

 iron best calculated to resist impact. There were three qualities 

 required : first, that the iron should not be crystalline, but, second, 

 that it should be of great tenacity and ductility, and, third, that it 

 should be very fibrous. Mr. Fairbairn produced specimens of spher- 

 ical and flat-ended shot, and proceeded to give the statical resistance 

 of each. 



The mean statical resistance to crushing of the two flat-ended speci- 

 mens of cast iron is 55.32 tons per square inch. The mean resistance 

 of the two round-ended specimens is 26.87 tons per square inch. The 

 ratio of resistance, therefore, of short columns of cast iron with two 

 flat ends to that of columns with one flat and one round end is as 

 55.32 to 26.87, or as 2.05 to 1. Applying this same rule to the steel 

 specimens, it would appear that the flat-ended shot would have sus- 

 tained a pressure of 180 tons per square inch before fracture. In the 

 experiment it actually sustained 120 tons per square inch without 

 injury, excepting a small permanent set. In the experiments with 

 cast iron the mean compression per unit of length of the flat-ended 

 specimens was .0665, and of the round-ended .1305. The ratio of 

 the compression of the round-ended to the flat-ended was, therefore, 

 as 1.96 : 1, or nearly in the inverse ratio of the statical crushing pres- 

 sures. Applying this law to the case of the steel flat-ended speci- 

 men, we may conclude that the compression before fracture would 

 have been only .058 per unit of length. The determination of the 

 statical crushing pressure of the flat-ended steel shot as 180 tons per 

 square inch and its compression as .058, is important, on account of 

 the extensive employment of shot of this material, size, and form in 

 the experiments at Shoeburyness. In the case of the lead specimens, 

 the compression with equal weights was the same, whether the speci- 

 men were at first round-ended or flat-ended. This is accounted for 

 by the extreme ductility of the metal and the great amount of com- 

 pression sustained. In regard to the wrought-iron specimens, it may 

 be observed that no definite result is arrived at, except the enormous 



