ID FAHADAY 



round the globe how they fall round the surface, giving 

 roundness to it, clothing it like a garment ; but, besides that, 

 there are other properties of water. Here, for instance, is 

 some quicklime, and if I add some water to it, you will 

 find another power and property in the water. (') It is now 

 very hot; it is steaming up; and I could perhaps light 

 phosphorus or a lucifer-match with it. Now that could not 

 happen without a force in the water to produce the result; 

 but that force is entirely distinct from its power of falling 

 to the earth. Again, here is another substance [some anhy- 

 drous sulphate of copper (*)] which will illustrate another 

 kind of power. [The lecturer here poured some water over 

 the white sulphate of copper, which immediately became 

 blue, evolving considerable heat at the same time.] Here 

 is the same water with a substance which heats nearly as 

 much as the lime does, but see how differently. So great 

 indeed is this heat in the case of lime, that it is sufficient 

 sometimes (as you see here) to set wood on fire; and this 

 explains what we have sometimes heard, of barges laden 

 with quicklime taking fire in the middle of the river, in con- 

 sequence of this power of heat brought into play by a leakage 

 of the water into the barge. You see how strangely different 

 subjects for our consideration arise when we come to think 

 over these various matters the power of heat evolved by 

 acting upon lime with water, and the power which water has 

 of turning this salt of copper from white to blue. 



I want you now to understand the nature of the most sim- 

 ple exertion of this power of matter called weight or gravity. 

 Bodies are heavy; you saw that in the case of water when 

 I placed it in the balance. Here I have what we call a 

 weight [an iron half cwt.] a thing called a weight because 

 in it the exercise of that power of pressing downward is es- 

 pecially used for the purposes of weighing; and I have also 

 one of these little inflated India-rubber bladders, which are 



8 Power or property in water. This power the heat by which the water 

 fe kept in a fluid state is said, under ordinary circumstances, to be latent 

 &r insensible. When, however, the water changes its form, and, by uniting 

 with the lime or sulphate of copper, becomes solid, the heat which retained 

 it in a liquid state is evolved. 



* Anhydrous sulphate of copper: sulphate of copper deprived of its water 

 of crystallization. To obtain it the blue sulphate is calcined in an earthen 

 crucible. 



