162 COSMOS. 



after considerable periods of time, that the three variable 

 elements of the total force of terrestrial magnetism caused 

 either an alteration in the direction of the axes, or that such 

 small systems of magnetic forces were at least apparently 

 independent of these influences. 



II. 



Reaction of the interior of the Earth upon its surface ; mani- 

 festing itself : a. Merely dynamically, by tremulous un- 

 dulations (earthquakes] ; b. By the high temperature of 

 mineral springs, and by the difference of the intermixed 

 salts and gases (Thermal springs); c. By the outbreak of 

 elastic fluids, sometimes accompanied by phenomena of 

 spontaneous ignition (ffas and mud volcanoes, burning 

 naphtha springs, Salses) ; d. By the grand and mighty 

 actions of true volcanoes, which (when they have a perma- 

 nent connexion with the atmosphere by fissures and craters) 

 throw up fused earth from the depths of the interior, partly 

 only in the form of red-hot cinders, but partly submitted to 

 varying processes of crystalline rock formation, poured out 

 in long, narrow streams. 



In order to maintain, in accordance with the fundamental 

 plan of this work, the co-ordination of telluric phenomena 



sultant upon the intensity of the polar force, I considered the small 

 particles to be so many small magnets. Seethe new vieAvs regarding this 

 subject in a treatise by Melloui, read by that distinguished physicist 

 before the Royal Academy at Naples, in the month of January, 1853 

 (Esperienze intorno al Magnetisms delle Rocche, Mem. i, Sulla Polarita). 

 The popular notion which has been so long current, more especially on 

 the shores of the Mediterranean, that if a magnetic rod be rubbed with 

 an onion, or brought in contact with the emanations of the plant, the 

 directive force will be diminished, while a compass thus treated would 

 mislead the steersman, is mentioned in Prodi Diadoclii Paraphrases 

 Ptolem. libriiv. deSideruma/ectionibus, 1635, p. 20 (Delambre, Hist.de 

 I' Astronomic Ancitnne, t. ii, p. 545). It is difficult to conceive what 

 could have given occasion to so singular a popular error. 



