268 Scientific Reviews. 



ter, and even when pressed to the bottom of a pot of liquid metal, it rises to the 

 top. These phenomena indicate that we are not acquainted with the specific 

 gravity of iron, when it is not affected by the terrestrial magnetism." 



We know not upon what authority Mr. M'V. makes this state- 

 ment as to the volume of cold cast iron, but Ave should have thought 

 that the circumstance of its swimming on melted iron would have 

 led him at once, without hesitation, to an opposite conclusion. For 

 the fact is, that cast iron is classed with ice, bismuth, antimony, 

 and most saline solutions which occupy a greater space when in 

 the solid or crystallized, than when in the liquid state, being ex- 

 ceptions to the general law of expansion by change from the solid 

 to the liquid state ; and it is to this very property that iron owes 

 its great utility in founding. Its expansion on cooling causes it to 

 take a good impression, and thus the most delicate figures may be 

 cast in iron, while in gold or silver they must be struck. 



There are many other topics discussed in the work under review, 

 into the consideration of which we should have been happy to ac- 

 company our author. But we have already trespassed beyond our 

 usual space. In the meantime, having done so much for theory, we 

 would urge Mr. M'V. to turn his attention to experiment, and his 

 opinions will speedily undergo modification. It is not impossible to 

 combine large views with minute experimental research, (though it is 

 stated by Mr. M'V. that " to limit our researches by actual experi- 

 ment, is to exclude ourselves from the inquiry ;") but we think it 

 is impossible now for any one so to master the wide field of science, 

 "rambled over in the volume before us, as to enable him to lay down 

 the law of nature in regard to her most minute and most abstruse 

 phenomena. We are not averse to a little theory : it is, on the 

 contrary, pleasant and refreshing, as connecting at once and 

 relieving the dryness of mere experimental results ; but it must 

 be rational and chastened theory, such as is derived from experi- 

 ment, as waters from a fountain, and which, like the stream 

 skirting the mountain ridge, shall at every step receive fresh acces- 

 sions from similar sources ; and, disappearing not for a time like 

 the fabled rivers of classic Greece, — not losing itself utterly among 

 sands as in eastern deserts, shall preserve a continuous and unbro- 

 ken course, showing a manifest and consecutive connection with 

 its parent spring, till it reach its legitimate and final destina- 

 tion. From other theory than this, it is the boast of our age to 

 ^ave escaped, and the splendid results due to the inductive method, 

 must be forgotten ere it will trust itself again to the sophism of a 

 priori speculation. 



