428 NATURE'S TEACHINGS. 



little glass machine for dispersing perfumes in the form of 

 spray. In cases of headache it is almost invaluable, the spray 

 cooling the heated forehead like magic, and at the same time 

 filling the room with the grateful perfume. 



It has even a greater claim to human gratitude, as I 

 can personally testify. I have the strongest objection to a 

 surgeon's knife, especially when I know, from sad experience, 

 that he is going to make very free use of it. But, on the last 

 occasion, I cared nothing for it, owing to the happy invention 

 called Ether Spray. 



The effects were remarkable. First, a delicious cooling of a 

 spot raging with internal fires. Then it was rather colder than 

 I liked. Then it was much colder than I liked. Then it 

 became almost too cold to bear, reminding me of my child- 

 hood's feet on the outside of the Birmingham coach in the 

 depth of winter. 



Suddenly all sensation ceased, and the skin became white as 

 parchment. Out came the surgeon's bistoury, and I looked at 

 him with as calm composure as if he had been whittling a deal 

 plank. There was absolutely no feeling whatever, the local 

 nerves having been temporarily frozen, so great is the power of 

 evaporation. If it ever be my lot again to endure cold steel, I 

 shall have the ether spray. 



ON the extreme right of the illustration is seen the " Wet- 

 bulb " Thermometer, which carries out the same principle, the 

 thermometer being double, and one bulb being covered with a 

 wet envelope, while the other is dry. 



Below is one of the many inventions for making artificial ice, 

 all of them depending on the cooling power of evaporation. 

 Perhaps some of my readers may have seen molten iron poured 

 over the human hand without doing the least harm, or 

 mercury frozen in a red, or rather a white, hot vessel. Both 

 these phenomena are due to the cooling power of evaporatioE, 

 which is made to act with extreme rapidity, and so absorbs the 

 heat until even mercury is rendered solid, and can be cast in a 

 mould like a leaden bullet. 



IN the accompanying illustration we have an example of the 

 Condensating principle as applied to the steam-engine, and 



