REP 



REP 



trenched, but also, in a certain space of 

 tin e, grows equal to it. Hence it is that 

 we frequently see lobsters which have 

 their two large legs unequal in all pro- 

 p< tions. And if the part reproduced be 

 br ken off, a second will succeed. 



REPTILIA, in natural history, an order 

 of Amphibia, the character of which is, 

 that they breathe through the mouth; 

 have feet, and flat naked ears without 

 auricles. There are five genera, viz. 



Draco 



Lacerta 

 Itana 



Siren 

 Tertudo. 



REPULSION, in physics, that property 

 in bodies, whereby, if they are placed 

 just beyond the sphere of each other's 

 attraction of cohesion, they mutually fly 

 from each other. Thus, if an oily sub- 

 stance, lighter than water, be placed on 

 the surface thereof, or if a piece of iron 

 be laid upon mercury, the surface of the 

 fluid will be depressed about the body 

 laid on it : this depression is manifestly 

 occasioned by a repelling power in the 

 bodies, which hinders the approach of 

 the fluid towards them. But it is pos- 

 sible, in some cases, to press or force the 

 repelling bodies into the sphere of one 

 another's attraction ; and then they will 

 mutually tend towards each other, as 

 when we mix oil and water till they in- 

 corporate. Dr. Knight defines repulsion 

 to be that cause which makes bodies mu- 

 tually endeavour to recede from each 

 other, with different forces, at different 

 times ; and that such a cause exists in na- 

 ture, he thinks evident, for the following 

 reasons. 1. Because all bodies are elec- 

 trical, or capable of being made so ; and 

 jt is well known, that electrical bodies 

 both attract and repel. 2. Both attrac- 

 tion and repulsion are very conspicuous 

 in all magnetical bodies. 3. Sir Isaac 

 Newton has shown from experiments, 

 that the surfaces of two convex glasses 

 repel each other. 4. The same great 

 philosopher has explained the elasticity 

 of the air, by supposing its particles mu- 

 tually to repel each other. 5. The par- 

 ticles of light are, in part at least, re- 

 pelled from the surfaces of all bodies. 

 6. Lastly, it seems highly probable, that 

 the particles of light mutually repel each 

 other, as well as the particles of air. The 

 same gentleman ascribes the cause of re- 

 pulsion, as well as that of attraction, to 

 the immediate effect of God's will ; and 

 as attraction and repulsion are contraries, 

 and consequently cannot, at the same 



time, belong to the same substance, the 

 doctor supposes there are in nature two 

 kinds of matter, one attracting, the other 

 repelling ; and that those particles of 

 matter which repel each other, are sub- 

 ject to the general law of attraction in 

 respect of other matter. A repellent 

 matter being thus supposed, equally dis- 

 persed through the whole universe, the 

 doctor attempts to account for many na- 

 tural phenomena by means thereof He 

 thinks light is nothing but this repellent 

 matter put into violent vibrations, by the 

 repellent corpuscles which compose the 

 atmosphere of the sun and stars : and 

 that, therefore, we have no reason to be- 

 lieve they are gulphs of fire, but, like 

 the rest of the heavenly bodies, inhabita- 

 ble worlds. From the same principles, 

 he attempts to explain the nature of lire 

 and heat, the various phenomena of the 

 magnet, and the cause of the variation of 

 the needle : and, indeed, it is difficult, if 

 not impossible, by the doctrine of attrac- 

 tion alone, to account for all the pheno- 

 mena observable in experiments made 

 with magnets, which may now be solved 

 by admitting this doctrine of a repellent, 

 fluid ; but whether it will be sufficient to 

 account for all the particular phenomena 

 of nature, which are the proper tests of 

 an hypothesis, time and experience alone 

 must determine. The doctor also endea- 

 vours to show, that the attractions of co- 

 hesion, gravity, and magnetism, are the 

 same, and that by these two active prin- 

 ciples, viz. attraction and repulsion, all 

 the phenomena of nature may be explain- 

 ed ; but as his ingenious treatise on this 

 subject is laid down in a series of propo- 

 sitions, all connected together, it would 

 be impossible to do justice to his argu- 

 ments without transcribing the whole : 

 we shall therefore refer the curious to the 

 book itself 



According to 'sGravesande and others, 

 when light is reflected from a polished 

 spherical surface, the particles of light 

 do not strike upon the solid parts, and so 

 rebound from them ; but are repelled 

 from the surface, at a small distance before 

 they touch it, by a power extended all 

 over the said polished surface. And Sir 

 Isaac Newton observes, that the rays of 

 light are also expelled by the edges of 

 bodies, as they pass near them ; so as to 

 make their shadows, in some cases, lar- 

 ger than they would otherwise be. 



REPULSION, in chemistry. Sir Isaac 

 Newton demonstrated, that if this law be 

 correct, then the force, by which the 

 particles of air recede from each other, 



