ATMOSPHERIC ELECTRICITY. 513 



monocotyledonous ones which he observed. Omitting particulars, the 

 cuts (Fig. 17) will show the effects produced in four instances. 



In the case of A, the apex of the radicle is so much bent away 

 from the square as to form a hook. At B, the irritation of the card, 

 aided, perhaps, by geotropism, has formed a circle. At C, the tip in 

 forming a loop has rubbed off the attached bit, and the circle has con- 

 tracted, while at D, the apex, in making a second turn, passed through 

 the first loop and so rubbed off the card, and, growing downward, tied 

 itself into a knot. 



Mr. Darwin believes that the tips of all radicles are similarly sen- 

 sitive, and transmit an influence causing the upper part to bend. 

 Moreover, the tip distinguishes between harder and softer objects, and 

 between moisture and dryness. It is also sensitive to light and gravi- 

 tation, and the course of the radicle in the ground is determined by 

 the tip. The volume concludes with the following sentence : " It is 

 hardly an exaggeration to say that the tip of the radicle thus en- 

 dowed, and having the power of directing the movements of the ad- 

 joining parts, acts like the brain of one of the lower animals ; the 

 brain, being seated within the anterior end of the body, receiving im- 

 pressions from the sense-organs and directing the several movements." 







ATMOSPHEKIC ELECTRICITY. 



By Peofessoe H. S. CAEHAET. 



FROM the earliest periods the flash of lightning and the peal of 

 thunder have excited curiosity, stimulated awe, and inspired fear 

 in man ; and according to his mythological, religious, or poetic habit 

 of mind has he regarded the latter as the bolt of Jove, the voice of 

 God, or the conscious utterance of the heavens. The explanation of 

 these appearances in the sky is most curious and fantastic, even after 

 the introduction of the modern inductive method. In ^ " Compendi- 

 ous System of Natural Philosophy," by J. Rowning, M. A., London, 

 1744, we find the following : " As vapors exhaled from the surface of 

 water are carried up into the atmosphere, in like manner the effluvia 

 of solid bodies are continually ascending thither. Now, we find by ex- 

 periment that there are several inflammable bodies which, being mixed 

 together in due proportion, will kindle into flame by fermentation 

 alone, without the help of any fiery particles. When, therefore, there 

 happens to be a mixture of the eftiuvia of such bodies floating in the 

 air, they ferment, kindle, and, flashing like gunpowder, occasion those 

 explosions and streams of fire which we call thunder and lightning." 



Ever since Franklin identified lightning with the electricity of the 

 frictional machine, an inquiry has been prosecuted into the origin of 

 VOL. xvin. 33 



