44 OBJECTS, ADVANTAGES, AND 



substance ; that acids should be almost all formed of different kinds of 

 air, and that one of those acids, whose strength can dissolve almost 

 any of the metals, should be made of the self-same ingredients with 

 the common air we breathe ; that salts should be of a metallic nature 

 and composed, in great part, of metals, fluid like quicksilver, but 

 lighter than water, and which, without any heating, take fire upon 

 being exposed to the air, and, by burning, form the substance so 

 abounding in saltpetre and in the ashes of burnt wood : these, surely, 

 are things to excite the wonder of any reflecting mind nay, of any 

 one but little accustomed to reflect. And yet these are trifling when 

 compared to the prodigies which Astronomy opens to our view : the 

 enormous masses of the heavenly bodies ; their immense distances ; 

 their countless numbers, and their motions, whose swiftness mocks the 

 uttermost efforts of the imagination. 



Akin to this pleasure of contemplating new and extraordinary truths, 

 is the gratification of a more learned curiosity, by tracing resem- 

 blances and relations between things, which, to common apprehen- 

 sion, seem widely different. Mathematical science to thinking minds 

 affords this pleasure in a high degree. It is agreeable to know that 

 the three angles of every triangle, whatever be its size, howsoever its 

 sides may be inclined to each other, are always of necessity, when 

 taken together, the same in amount : that any regular kind of figure 

 whatever, upon the one side of a right-angled triangle, is equal to the 

 two figures of the same kind upon the two other sides, whatever be the 

 size of the triangle : that the properties of an oval curve are extremely 

 similar to those of a curve, which appears the least like it of any, 

 consisting of two branches of infinite extent, with their backs turned 

 to each other. To trace such unexpected resemblances is, indeed, the 

 object of all philosophy ; and experimental science in particular is ' 

 occupied with such investigations, giving us general views, and . 

 enabling us to explain the appearances of nature, that is, to show how * 

 one appearance is connected with another. But we are now only con- 

 sidering the gratification derived from learning these things. It is 

 surely a satisfaction, for instance, to know that the same thing, or 

 motion, or whatever it is, which causes the sensation of heat, causes 

 also fluidity, and expands bodies in all directions ; that electricity, the 

 light which is seen on the back of a cat when slightly rubbed on a 

 frosty evening, is the very same matter with the lightning of the 

 clouds ; that plants breathe like ourselves, but differently by day and 

 by night ; that the air which burns in our lamps enables a balloon to 

 mount, and causes the globules of the dust of plants to rise, float 

 through the air, and continue their race ; in a word, is the immediate 

 cause of vegetation. Nothing can at first view appear less like, or 

 less likely to be caused by the same thing, than the processes of burning 

 and of breathing, the rust of metals and burning, an acid and 

 rust, the influence of a plant on the air it grows in by night, and of 

 an animal on the same air at any time, nay, and of a body burning in 

 that air ; and yet all these are the same operation. It is an unde- 

 niable fact, that the very same thing which makes the fire burn, makes 

 metals rust, forms acids, and causes plants and animals to breathe ; 



