of the British Association to the meeting at Glasgow 1840. 483 



siderable delicacy, failed to detect, in these seemingly favour- 

 able circumstances, any electrical current. 



The extensive and rapidly increasing applications of iron 

 to public and private structures of all kinds in which durabi- 

 lity of material is a first requisite, have made it highly desirable 

 to possess accurate information respecting the nature of the 

 chemical forces which effect the destruction of this hard and 

 apparently intractable metal. The preservation of iron from 

 oxidation and corrosion is indeed an object of paramount im- 

 portance in civil engineering. The Association was, therefore, 

 anxious to direct inquiry to this subject, and gladly availed it- 

 self of the assistance of Mr. Mallet, a gentleman peculiarly 

 qualified for such investigations, both from his knowledge as a 

 chemist, and from his opportunities of observation as a prac- 

 tical engineer. An extensive series of experiments has ac- 

 cordingly been instituted by him, with the support of the 

 Association, on the action of sea and river water, in differ- 

 ent circumstances as to purity and temperature, upon a large 

 number of specimens of both cast and wrought iron of different 

 kinds. These experiments are still in progress, and the effects 

 are observed from time to time. They will afford valuable 

 data for the engineer, and form the principal object of the in- 

 quiry ; but a period of a few years will be required for its 

 completion. In the meantime, Mr. Mallet has furnished a 

 report on the present state of our knowledge of the subject, 

 drawn from various published sources, and from his own ex- 

 tensive observations. In this report he examines very fully 

 the general conditions of the oxidation of iron, and how this 

 operation is greatly promoted, although modified in its results, 

 by sea-water ; also in what manner the tendency to corrosion 

 is affected by the composition, the grain, porosity, and other 

 mechanical properties of the different commercial varieties of 

 iron. The influence of minute quantities of other metals, in 

 imparting durability to iron, is also considered. Mr. Mallet 

 devotes much attention to the consequences of the galvanic as- 

 sociation of different metals with iron, a subject of recent in- 

 terest from the applications of zinc and other metals to 

 protect iron, which are at present agitated. He concludes 

 this, his first report, by recommending a series of inquiries, 

 ten in number, which will supply the desiderata immediately 

 required by the engineer and by the chemist. 



We have next to notice a report by Professor Powell, on 

 the present state of our knowledge of refractive Indices for 

 the standard rays of the solar spectrum in different media. 

 The difficulty which the fact of the dispersion of light has 

 offered to the universal application of the undulatory theory, 



212 



