MECHANICS AND USEFUL ARTS. 99 



the English scientific circles, and Dr. Noad has recently made public some 

 results attained in experimenting at the Welsh iron mines of great interest, 

 considering how extensively iron is now used for bridges, cables, and sup- 

 ports. Dr. Noad says: "The tendency of iron to pass from the fibrous or 

 tough to the crystalline or brittle condition is promoted by various causes ; 

 every thing, in fact, which occasions a vibration among its particles has this 

 tendency." He then describes his experiments, which prove that the metal 

 may be made to pass from one state to the other : ' ; Seeing a large quantity 

 of iron chain lying about, and learning that, though scarcely worn, it had 

 been laid aside in consequence of the breaking of some of the links, I ex- 

 amined several from different parts of the chain. I found that a single smart 

 blow with a hammer was sufficient to snap the metal, the fracture of which 

 was crystalline, and its brittleness such that it could without difficulty be 

 broken into small pieces under the hammer. I now heated strongly in a 

 forge some of the broken links, and allowed them to cool very slowly under- 

 neath a bed of fine sand. After the lapse of 24 hours they were examined ; 

 the metal was found to have recovered its tenacity, it could no longer be 

 broken to pieces under the hammer ; and when at length, after repeated 

 heavy blows, it did partially yield, the texture of the metal was found to be 

 perfectly fibrous every trace of a crystalline structure had disappeared." 

 Dr. Noad thinks that the iron of the Nasymth gun has been crystallized by 

 continuous hammering ; and he suggests that its fibrous condition may be re- 

 stored by annealing. 



ARTILLERY AND PROJECTILES. 



In a discussion which occurred at the last meeting of the British Asso- 

 ciation on the subject of artillery and projectiles, Dr. Scoresby stated, as 

 the results of experiments he had made, that the quality of iron might be 

 effectually tested by its effect in counteracting the deviation produced on a 

 compass by a magnet placed in opposition to it. Mr. Neilson, iron-founder, 

 gave, as the result of Ms experience, that, if repeatedly heated, or heated 

 without being subjected to severe hammering or pressure, the center of a mass 

 of iron was sure to become crystalline and friable. Mr. Rennie thought the 

 defects of the artillery of the present day were, in a great degree, to be attri- 

 buted to the competition in cheapness among manufacturers. Sir E. Belcher 

 stated that, in engagements which he had witnessed, much more severe than 

 that of Sweaborg, no accidents whatever had occurred to the ordnance. He 

 suggested the employment of guns similar to those of the Chinese, with strong 

 cast-iron breeches, the direction-tube being a matter of little moment. 



Mr. Robinson stated that rifled guns are more liable to burst, because the 

 force necessary to explode a ball from such a piece of ordnance is much greater 

 than that required for a plain bored gun ; and also that a rifled gun is much 

 more liable to burst or be rendered useless from frequent discharges, because 

 of the force necessary to cause rotation having to be added to that which 

 causes projection. Dr. Robinson alluded to the bronze guns of the Darda- 

 nelles, which are of three feet bore, used against our fleets not many years 



