DENSITY OF THE EARTH. 171 



entirely opposite views regarding the nature of the interior of 

 the globe. It has been computed at what depths liquid or 

 even gaseous substances would, from the pressure of their 

 own superimposed strata, attain a density exceeding that of 

 platinum or even iridium ; and in order that the compression 

 which has been determined within such narrow limits migh* 

 be brought into harmony with the assumption of simple and 

 infinitely compressible matter, Leslie has ingeniously conceived 

 the nucleus of the world to be a hollow sphere, filled with an 

 assumed " imponderable matter, having an enormous force of 

 expansion." These venturesome and arbitrary conjectures 

 have given rise, in wholly unscientific circles, to still more 

 fantastic notions. The hollow sphere has by degrees been 

 peopled with plants and animals, and two small subterranean 

 revolving planets — Pluto and Proserpine — were imaginatively 

 supposed to shed over it their mild light ; as, however, it was 

 further imagined that an ever-uniform temperature reigned in 

 these internal regions, the air, which was made self-luminous 

 by compression, might well render the planets of this lower 

 world unnecessary. Near the north pole, at 82° latitude, 

 whence the polar light emanates, was an enormous opening, 

 through which a descent might be made into the hollow 

 sphere, and Sir Humphrey Davy and myself were even pub- 

 licly and frequently invited by Captain Symmes to enter upon 

 this subterranean expedition : so powerful is the morbid in- 

 clination of men to fill unknown spaces with shapes of won- 

 der, totally unmindful of the counter evidence furnished by 

 well-attested facts and universally acknowledged natural laws. 

 Even the celebrated Halley, at the end of the seventeenth 

 century, hollowed out the Earth in his magnetic speculations I 

 Men were invited to believe that a subterranean freely-ro- 

 tating nucleus occasions by its position the diurnal and an- 

 nual changes of magnetic declination. It has thus been at- 

 tempted in our own day, with tedious solemnity, to clothe in 

 a scientific garb the quaintly-devised fiction of the humorous 

 Ilolberg.* 



* [The work referred to, one of the wittiest prodnctions of tlie learned 

 Norwegian satirist and dramatist Holberg, was written in Latin, and 

 first appeared under the following title : Nicolai Klimii Her suhterra- 

 neum novum tellvris theonam ac historiam qr/intce monarchice adhuc «o- 

 his incogvAtce exhibens e hibliotheca b. Abelini. Hafniee ct Lipsice snmt. 

 Jac. Prenss, 1741. An admirable Danish translation of this learned 

 but severe satire on the institutions, morals, and manners of the inhab* 

 itants of the upper Earth, appeared at Copenhagen in 1789, and was 

 entitled Niels Klim^s ujiderjordiske reise ved Lndwig Holberg, oversat 



