On Elastic'ity. 149 



change, it is plain that when the external force is removed 

 it must resume its first position in the mass, and, by doino- 

 so, restore it to its former figure, in effectinij which the af- 

 finity of aggregation co-operates ; for we have been sup- 

 posing such a force only applied as could change the form, 

 while applied, without overcoming the aggregation of the 

 mass. 



The vibrations which follow, if the sprina; be left quite 

 iret after force has been applied, may be expfamed in a way 

 perfectly similar to what we have already laid down when 

 speaking of a bar struck by a hammer. The caloric beina; 

 put in motion, a larger quantity of it runs from the plus 

 side to the side that was minus than the atlinity of the latter 

 demands, and is therefore driven back again, and so alter- 

 nately, till by little and little it ceases its motion as equili- 

 brium comes to be established. 



After the bar AB has by any applied force been brouoht 

 into the form CD, the caloric, which in the natural st^ue 

 of the bar resided between b and (/, having been forced to 

 find lodging-room towards ac on the side now rendered 

 convex, and the lines ah and cd, or the portions of metal 

 which they represent, being brought into contact in the 

 point e; or, if the possibility of the perfect contact of the 

 nioleculae be denied, as nearly into contact as possible in 

 the point e ; then the said point e (and so of any other point 

 of the concave surface) becomes a fulcrum over which the 

 bar may be broken if an increased force be applied ; for 

 all the caloric that can be removed by mechanical means 

 from the concave side having been transferred to some more 

 convex part of the bar, it must follow, as a consequence, 

 that any attempt to make the metallic matter enter spaces 

 already occupied by metallic matter must be vain, and can 

 only operate to draw the moleculoe on the convex side to 

 such a distance from each other as to admit foiciirn matter 

 between them, viz. the atmosphere or other surrounding 

 medium, after which it will be impossible lor them to coa- 

 lesce again. 



In this way would we account for that effect which has 

 hitherto been ascribed to the nioleculae being remo\cd to 

 such a distance from each other as to place them b' vo.id 

 each others sphere of attraction. It is true thev are broiiLil.t 

 into such a situation that their attractive aliinily canuftt 

 again unite them as an aggregate ; but we think iheir attrac- 

 tion is not annihilated, as the common mode of expression 

 may suggest to those who do not properly examine the 

 nialtcr. There is only a new affinity brought into j)Iav^ 

 K3, VIS. 



