14 FARADAY 



down. How pretty that is! I poured nothing in but the 

 invisible steam, or vapor, or gas which came from the mar- 

 ble, but you see that part of the marble, although it has 

 taken the shape of air, still gravitates as it did before. Now 

 will it weigh down that bit of paper? [placing a piece of 

 paper in the opposite scale]. Yes, more than that; it nearly 

 weighs down this bit of paper [placing another piece of 

 paper in]. And thus you see that other forms of matter 

 besides solids and liquids tend to fall to the earth ; and, there- 

 fore, you will accept from me the fact that all things gravi- 

 tate, whatever may be their form or condition. Now here is 

 another chemical test which is very readily applied. [Some 

 of the carbonic acid was poured from one vessel into another, 

 and its presence in the latter shown by introducing into it a 

 lighted taper, which was immediately extinguished.] You 

 see from this result also that it gravitates. All these experi- 

 ments show you that, tried by the balance, tried by pouring 

 like water from one vessel to another, this steam, or vapor, 

 or gas is, like all other things, attracted to the earth. 



There is another point I want in the next place to draw 

 your attention to. I have here a quantity of shot; each of 

 these falls separately, and each has its own gravitating 

 power, as you perceive when I let them fall loosely on a 

 sheet of paper. If I put them into a bottle, I collect them 

 together as one mass, and philosophers have discovered that 

 there is a certain point in the middle of the whole collection 

 of shots that may be considered as the one point in which 

 all their gravitating power is centred, and that point they 

 call the centre of gravity; it is not at all a bad name, and 

 rather a short one the centre of gravity. Now suppose I 

 take a sheet of pasteboard, or any other thing easily dealt 

 with, and run a bradawl through it at one corner, A 

 (Fie. 3), and Mr. Anderson holds that up in his hand before 

 us, and I then take a piece of thread and an ivory ball, 

 and hang that upon the awl, then the centre of gravity of both 

 the pasteboard and the ball and string are as near as they 

 can get to the centre of the earth; that is to say, the 

 whole of the attracting power of the earth is, as it were, 

 centred in a single point of the cardboard, and this point 

 is exactly below the point of suspension. All I have to da, 



