PNEUMATICS. 



185 



perfectly constant, it is nec- 

 casary that the difference 

 of lengths of the columns of 

 liquid in both branches 

 should be immovable. 

 Thia may be effected by 

 connecting the sj^Dhon with 

 a float and pulley, aa is 

 ■pepresented in Fig. 181. 



The curi- 



Fio. 181. 



Explain the 

 phenomenon 

 of intermitting 

 springs. 



ous pheno- 

 menon of 

 intermitting 

 springs may be explained 

 upon the principle of the 

 syphon. These springs run 

 for a time and then stop ^-: 

 altogether, and after a time 

 run again, and then stop. 

 If we suppose a reservoir 

 in the interior of a hiU or 

 mountain, with a syphon- 

 like channel running from it, as 

 in Fig. 182, then as soon as the 

 water collecting in the reservoir 

 rises to the height shown by the 

 dotted line, the stream will be- 

 gin to flow, and continue flow- 

 ing till the reservoir is nearly 

 emptied. Again, after an in- 

 terval long enough to fill the 

 reservoir to the required height, 

 it will again flow, and so on. 



When wui a ^^^- ^^ ^ solid substancG have the same 

 MsJendeT'^iS density as atmospheric air, it will, when im- 

 the air? merscd in air, lose its entire weight, and will 



remain suspended in it in any position in which it may 

 be jjlaced. 

 ^ .„ 397. If a solid body, bnlk for bulk, be lighter 



When mil a .... , it. 



hody rise in than atmosplieric air, it is pressed upward by 

 the surrounding particles of air, and rises, upon 

 the same principle as a cork rises from the bottom of a 

 vessel of water. (See § 85.) 



