PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 397 



" At present there is a great excitement in Mariposa, from the recent 

 discovery of very valuable silver and gold veins, which thus far surpass \u 

 ' richness any heretofore found. Large quantities of the ore have been sent 

 to San Francisco for assay. The silver has turned out at the rate of $500 

 per ton; the gold much beyond that figure; and, as they dig down, the 

 richer it becomes. Speculators from San Francisco are here in squads, 

 buying up the various interests. Tlie discoverer is entitled to 500 feet of 

 front, r,unning back as far as the vein extends; all other claimants are | 

 entitled to 250 feet, and as it requires a large outlay of money to construct 

 mills and machinery, none but great capitalists can profit much by this 

 discovery, except by selling their interests to the best advantage to others, 

 and in this way large fortunes are being made. My sons have some 

 valuable claims." 



The regular subject, "Iron-plated Ships," was then taken up. 



Mr. Fisher.— As I proposed this question, 1 suppose it devolves on me 

 to open the discussion with the remarks that I have to make. It has been 

 found, in England, that solid plates are better than armor made of several 

 thin plates. If the plate is solid and the iron is good, the force is expended 

 in altering the form of the shot, but if the plate is weak, that gives way, 

 and the form of the shot is not changed. It has been found that wrought 

 iron shot is not as good as cast iron, and it is now proposed to make the 

 shot of steel. The main office of these plates is to keep out shells, as solid 

 shot are not very destructive. Mr. Whitworth has sent a shell through a 

 target like the side of the Warrior; the shell passing through the plate 

 and bursting in the target, tearing it to pieces. The novel thing about 

 this shell was, that no arrangement was prepared for exploding the 

 charge; it was fired by the concussion of the projectile as it struck. It 

 could accordingly be handled with perfect safety, as dropping it, even into 

 the hold of a vessel, would not cause it to explode. 



Mr. Dibben.— What, then, caused it to explode when it struck ? 



Mr. Bartlett.— This is one of the manifestations of the conservation of 

 force. The heat is generated by the destruction of motion. The mechani- 

 cal force or motion is converted into caloric. 



Mr. Dibben. — These target experiments are calculated to mislead, from 

 the fact that the conditions under which they are made are very rarely 

 realized in practice. The gun is placed in a position exactly at right 

 angles with the target, the distance is short and is accurately known, and 

 consequently the penetration or destruction is much greater than it would 

 be in actual warfare. I think the plates yet have the advantage of the 

 guns. No practically successful wrought iron guns as large as 100-pound- 

 ers have ever been made in any considerable numbers, and the best gun 

 yet manufactured is the Parrott, or some one made on the same plan— that 

 is, a cast iron core with bands of wrought iron. Mr. Parrott has made a 

 large number of 200-pounder rifled cannon, and three which fire his shot 

 weig-hing 800 pounds, and the proof of all of these guns has been emi- 

 nently successful; the charge for the 100-pounders is one-tenth the weight 

 of the shot, but that for the 300-pounders is a little less than one-tenth. 

 So confident are Mr. Parrott and his men in the strength of these guns, 



