120 Ret?. J. B. Emmet t on the [Fes. 



Atomic expansion. 



Iron . 0-5634 



Gold 0-5685 



Copper 0-7644 



Silver 10427 



Tin M600 



Zinc 1-234 



Lead 1-389 



In this table, the atomic diameters are those marked with the 

 asterisk in Table 1. The order corresponds with that of their 

 fusibilities as nearly as can be expected ; for finding the expan- 

 sion of the metals is an operation of the greatest delicacy, and 

 one in which a small error may be committed by the most skilful 



3 / stoiTiic wcisht 



experimenter: besides, the atomic diameter = * / — r^ rr-- 



*^ ' A/ specific gravity' 



and in the calculations, until all the primary laws are fully deve- 

 loped, we have to suppose the particles of all solids to be simi- 

 larly situated, which certainly is not the case, and in solids, the 

 error may amount to one-fourth the gravity ; but since the metals 

 are all fusible, and with the exception of few at a moderate tem- 

 perature, compared w ith tlie total scale of heat which can be 

 produced, the error will not be so great. If the table be extended 

 to silex and other highly infusible substances, the general law is 

 very apparent. 



Upon the same principles many other properties of bodies 

 may be investigated and phenomena explained ; for example, it 

 a heated body be coated with different substances, the layer 

 being so thin as to produce no sensible effect by its conducting 

 power, the radiating power will be inversely as F ; for the caloric 

 is retained by the force of the surface only, and this power has 

 been shown to be greatest in the most highly electro-negative 

 bodies, or those which have the greatest tendency to the earth ; 

 and to this power that of radiation is inversely proportional : 

 this accords very well with experiment ; a heated clean metallic 

 surface has a radiating power of 12; covered with a thin coat 

 of glue, a highly positive body, it is 80 ; coated with lamp- 

 black 100. The reflecting powers of polished metals appear to 

 depend upon the density of the caloric contained in them, i. e. 

 to the capacity (or rather the specific heat, if it were known) of 

 equal volumes. The capacities of equal volumes are, iron 1*00, 

 brass -97, silver -84, tin -51, lead -45, which numbers do not 

 greatly difter from their powers of reflecting heat. 



The conducting powers of solids for heat depend primarily 

 upon the attraction and the capacity for heat ; this power is 

 nearly as the force F x capacity of equal volumes, if equal 

 lengtjis be used ; by computation the powers are, gold 75, 



