Lftson VIII. ] 



NATURAL PHILOSOPHY. 



21 



QUESTIO 



/."What is meant by the ATTRAC- 

 TION ov CO 



It is that power which causes parti- 

 cles of matter to stick together, or cohere ? 



T. Are all bodies kept together by 

 this power ? 



P. Yes ; but it is much stronger in 

 (tome bodies than in others. It is stronger, 

 or more powerful, in solid bodies, than in 

 fluids, and weakest in gaseous bodies. 



96. T. What is the effect of the influ- 

 ence of this power ? 



P. That some bodies are hard, others 

 tough, soft, brittle, elastic, and so on. 



/'. Is the attraction of cohesion 

 limited to the particles of the bodies ? 



P. No. It may exist between the 

 molecules of bodies, and between bodies 

 themselves ; and in the former case is 

 d molecular, or atomic attraction. 



98. T. Give me an example of mole- 

 cular attraction ? 



P. A piece of lump-sugar is kept to- 

 gether by molecular attraction, because 

 the atoms mutually attract each other; 

 and other bodies are operated upon in the 

 tame manner, in a greater or less degree. 



/'. Suppose that this force was not 

 exercised, what would be the result ? 



P. The bodies would be without form 

 or figure, and the molecules would be a 

 confused mass. 



100. T. Is actual contact necessary for 

 the exercise of this pro; 



P. No ; it acts at insensible distances, 

 the particles appear to us to touch 

 one another; but we learn, by means of the 

 microscope, that they do not 



101. 1 ' tint I break a stone 

 by a bl ninner, will the various 



ilcs unite a;- 



/'.No. The attraction of cohesion has 

 been overcome by the force of the blow ; 

 ;clcs have not sufficient mu- 

 tual attraction to unite again, indcj 

 of other causes. 



/'. Can you explain to me how it 



r dew, or a > 

 of mercury, unites and forms a sphere when 



it comes into contact with another body of 

 a similar nature ? 



P. Yes ; it is a law of nature, that the 

 particles of matter are attracted towards 

 a common centre, and therefore they ar- 

 range themselves thus. 



103. T. Can you give me a familiar 

 illustration of the attraction of cohesion ? 



P. You see that I have two pieces of 

 lend with flat and smooth surfaces. [Ex- 

 periment 16.] Press the surfaces firmly 

 together with a twist, and you will find 

 tint it will require a considerable force to 

 separate them. 



1 K T. If a sponge is placed in a plate 

 of water, what is the effect ? 



P. The greater part of the water is 

 drawn into the pores of the sponge by 

 capillary attraction. 



105. T. What do you mean by capil- 

 lary attraction ? 



/'.It is the force by which fluids nrc 

 r.UM-d above their levels, the attraction that 

 causes hair-like tubes to raise liquids. 



106. T. How can you illustrate this ? 

 P. I have here a ^. which 



contains some infusion of logwood, and 

 there is a piece of wood fitting to the 



' a a s 



/If. It. 



put. which has fis : ^hs* in it. 



ment 17.] Im; 



i in the li.juid. it will rise 

 in each t:;ln-. but will vary in tin- I). 



the liquid is raised ; 

 will not have any great hei> 

 bccau*! tube is in<- 



tanl from the circumference than ; 



