318 FRAGMENTS OF SCIENCE. 



scope, may, when examined by the method alluded to, pro- 

 duce not only sensible but striking effects upon the eye. 



I take, for instance, this bottle of water intended to 

 quench your lecturer's thirst. In the track of the beam it 

 simply reveals itself as dirty water. So you see that we 

 are invaded with dirt not only in the air we breathe, but 

 in the water we drink. And this Avater is no worse than 

 the other London waters. Thanks to the kindness of Pro- 

 fessor Frankland, I have been furnished with specimens of 

 the water of eight London companies. They are all laden 

 with impurities mechanically suspended. But you will ask 

 whether filtering will not remove the suspended matter ? 

 The grosser matter, undoubtedly, but not the more finely- 

 divided matter. Here is water which has been passed four 

 times through a filter of bibulous paper, but it is still laden 

 with fine matter. Here, also, is a bottle kindly sent me by 

 Mr. Lipscomb, and passed once through his charcoal filter. 

 But the track of the beam through it is more luminous 

 than through air, because the quantity of matter suspended 

 in the water is greater than that suspended in air. Here 

 is another specimen courteously sent to me by the Silicated 

 Carbon Company. All the grosser matter has been re- 

 moved, but it is thick with fine matter. Nine-tenths of the 

 light scattered by these particles is perfectly polarized in a 

 direction at right angles to the beam, and this release of 

 the particles from the ordinary law of polarization is a 

 demonstration of their smallness. I should say by far the 

 greater number of the particles concerned in this scattering 

 are wholly beyond the range of the microscope, and no or- 

 dinary filter can intercept them. There is an aesthetic 

 pleasure in the drinking of a glass of cold sparkling water, 

 and I fear these experiments will destroy this pleasure if 

 you ever enjoyed it. And it is next to impossible by arti- 

 ficial means to produce pure water. Mr. Hartley, for ex- 

 ample, some time ago distilled water while it was sur- 



