NATURAL PHILOSOPHY. 



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montese government, by whose direction he has completed his apparatus; 

 and is thus able to obtain for the military authorities, almost instantaneously, 

 and without the assistance of any of the usual surveying instruments, all the 

 necessary materials for the construction of a complete topographical plan. 

 The instrument is described as extremely simple and very portable; it being, 

 in fact, a circular or cylindrical camera, little more than a foot in diameter, 

 with a spherical lens in the centre. The sensitive paper is placed on a reel on 

 one side of the lens, from which it is slowly wound off, as the view is taken, 

 on to a similar reel on the other side. When one view is taken, which cm- 

 braces one-third of the horizon, the instrument is turned one-third of a revo- 

 lution on its axis, and another view is taken. The operation is then repeated, 

 and the panorama is completed. The reduction of the plan is of course made 

 in the house ; but it is rendered easy by special contrivances in the camera, 

 by which every thing is set off to a scale of heights, dimensions, and dis- 

 tances. Happily, the services of the instrument cannot be monopolized for 

 warlike purposes; and if it really can accomplish what is reported of it, a 

 most valuable addition will have been made to the materials at the service of 

 the arts of peace. London Literary Gazette. 



ON THE HEAT-CONDUCTING POWER OF METALS AND ALLOYS. 



Messrs. Grace Calvert and Richard Johnson, of England, have been for 

 some time engaged in a series of experiments to determine the relative heat- 

 conducting powers of metals in a perfectly accurate and reliable manner, in 

 order that a standard might be obtained from which calculations could in 

 future be made, the numbers at present in use being regarded as unreliable. 

 The following results thus far arrived at, have been communicated to the 

 Royal Society. Taking silver, which is the best conductor, as 1000, they 

 obtained the relative conducting powers of the following metals : 



The precision obtained by this process is such, that the authors were able 

 to determine the different conducting powers of the same metal, when rolled 

 or cast, as shown above. They were also able to appreciate the influence of 

 crystallization on conductibility ; for they found that the conducting power 

 of a metal was different when it was cast horizontally or vertically, from 

 the different directions which the axes of crystallization took under these 

 circumstances. 



The importance of having the metals as pure as the resources of chemistry 

 allow, is shown by the action which one per cent, of impurity exerts on the, 

 conductibility of a metal, in some cases reducing it one-fifth or one-fourth. 

 Copper alloyed with one per cent, of various metals, gave different conduct- 



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