NATURAL HISTORY. 169 



the fortifications and reconnoitring the camp of an ehemy, 

 which could not be approached by other means. The diffi- 

 culties, under which this species of navigation labours, ap- 

 pear at present to be insurmountable ; and the want of some 

 means to control and regulate the movements of the aerial 

 vessel is so essential, as to excite a fear that it cannot be sup- 

 plied. 



Questions. — 1. What is aerostation ? 2. What is the best form for 

 a balloon ? 3. What are the two kinds of balloons? 4. How is a 

 balloon filled with hydrogen gas ? 5. Who invented the first agro- 

 static machine, and what was the result ? 6. What discovery did 

 Cavendish make ? (Hydrogen gas is 14 times lighter than common air, 

 — see Lesson on water.) 7. Wliat afterwards occurred to Dr. Black .'' 

 8. What idea did Cavallo conceive .'' — what is ascribed to him .'' 9. 

 What discovery did the Montgolfiers make ? 10. Who was the first 

 aerial navigator ? 11. What was the next discovery in this science ? 

 12. What is said of the ascent of Mr. Blanchard ? 13. Describe the 

 experiment of Mr. Gamerln. 14. What was the fate of Rozier and 

 Romain .'' 15. What is said of the advantages which have been 

 derived from balloons .'' IG. Of the difficulties under which this spe- 

 cies of navigation labours.'' [Note. Small balloons may be made of 

 thin strips of bladder, or otJier membrane, glued together.] 



LESSON 75. 



Natural History. 

 Pellu'cid, clear, transparent, not opaque. 

 Those who with a philosophical eye have contemplated 

 the productions of Nature, have all, by common consent, di- 

 vided them into three great classes, called the Animal, the 

 Vegetable, and the Mineral or Fossil kingdoms. These 

 terms are still in general use, and the most superficial ob- 

 server must be struck with their propriety. Animals have 

 an organized structure which regularly unfolds itself, and is 

 nourished and supported by air and food ; they consequently 

 possess life, and are subject to death ; they are moreover 

 endowed with sensation, and with spontaneous, as well as 

 voluntary, motion. Vegetables are organized, supported by 

 air and food, endowed with life, and subject to death as well 

 as animals. They have in some instances spontaneous, 

 though we know not that they have voluntary motion. They 

 are sensible to the action of nourishment, air, and light, and 

 15 



