e 
80 3 Dr. Fothergill’s aceount of ice islands. 
3. That the arctic regions alone give birth to ice islands, and 
the liquefaction of the polar ices to the tides, as has been supposed, 
seems highly improbable. 
4, That the ice islands observed in the more temperate seas, where 
the temperature decreases downwards, may originate where least ex- 
pected, viz. at the bottom; especially where rocks and other con- 
ducting bodies overspread the surface. 
5. That the notion of central fire is groundless ; and that objec- 
tions, drawn from it, or volcanoes, are alike inadmissible. 
6. That ice in the open air evaporates even below the point of con- 
gelation, and that evaporation generates cold and accumulates ice 
in the curious cave of Grace Dieu most in summer. 
7. That the evils, occasionally produced by ice islands, are com- 
plained of, while their- beneficial effects on the animal and vegetable 
creation have hitherto passed unnoticed. 
8. That winds, blowing over them, temper the intense — of 
summer in the adjacent climates. 
9. That ice islands may be guarded against by vigilance, “art by 
ships well constructed. 
‘10. That the thermometer may be rnin ppomenenety useful 
in pointing out the approach of rocks, shoals, and shores ; but par- 
ticularly of ice islands a sme Gulph stream. 
11. That the barometer may also gt ntribut - nad that these 
instruments should jointly constitute a a pat “Of the nautical apparatus, 
and daily observations be noted in the journals. 
12. Finally, that by due attention to the above rules those danger- 
ous obstacles to navigation may be detected, which elude the magnet- 
ic needle and all other instruments; and thus might the art ot naviga- 
tion be improved, science promoted, and many disasters prevented. - 
