little practice, be excellently well determined by the quick or slower ignition of a single sulphur match tied to a stick and held in the centre of the oven.

397 Creosote boils.

442 Tin melts, most easily of the metals.

460 The surface of polished steel acquires a pale straw color, and takes a slight degree of "temper" when suddenly chilled.

476 Bismuth melts.

554 Phosphorus boils.

560 Spirit of turpentine boils.

570 Sulphur boils.

580 The surface of polished steel acquires an uniform

deep blue color, and when suddenly chilled, takes

a high "temper."

590 Sulphuric acid boils.

600 Linseed oil boils.

612 Lead melts.

635 Iron begins to show light of ignition in the dark. 660 Mercury boils.

680 Zinc melts.

752 Iron bright red in the dark.

800 Hydrogen burns.

802 Charcoal burns.

809 Antimony melts.

884 Iron red hot in twilight.

980 Iron red heat-Daniel.

1077 Iron visibly red in daylight-Wedgwood. 1141 Heat of a common parlor fire-Daniel. 1207 Iron blood red in daylight-Wedgwood. 1857 Heat of an enamelling furnace.

2897 The diamond burns.

4717 Silver melts. 5247 Gold melts.

For the higher furnace temperatures we can offer no measurement but those of Wedgwood's pyrometer, which is admitted to be far from a satisfactory one. A good pyrometer is a great desideratum in science.

8487 Working heat of plate glass.

10177 Flint glass furnace lowest heat.

11737 Carbonization of iron-steel manufacture.

12257 Liverpool ware baked.

12777 Lowest welding heat of iron.

13427 Greatest welding heat of iron.

13297 to 15637 Common sorts of China ware and porcelain

vitrified.

15897 Flint glass furnace strongest heat.

17327 Greatest heat of a common smith's forge.

17977 Cobalt melts.

20577 Nickel melts..

Hessian crucible fused.

21637 Iron melts.

21877 Manganese melts.

Best Chinese porcelain softened.

Nankin porcelain not softened.

23177 Platinum, molydena, tungsten, and the more refractory of the metals, melt.

Titanium most difficult to melt.

25127 Greatest heat observed.

The above table presents a scale of temperatures designed to show the control of temperature over the phenomena of nature and of art, in their widest range, from the solidification of the gases, the freezing of mercury and of water, to those delicate temperatures necessary to vegetable and animal life, existing on the landscape of Nature; and thence to those of the bleaching, boiling and baking temperatures,

and the furnace heats, from the melting of tin and lead, to those of the carbonization and welding heats of iron, and the melting of the metals most difficult of fusion.

Persons who have not given attention to the subject have no idea of the importance of certain precise temperatures to the best performance of many processes in the useful arts. A variation of five degrees will often not only render an operation ineffective, but partially or entirely destroy the materials employed. Certain temperatures are doubtless, in like manner, essential to all natural phenomena.

The table which follows is designed to show the effects of a comparatively small range of the natural atmospheric temperatures as they appear to affect the distribution on the earth's convex, of man the most sagacious of animals— and more especially the relation of climate to the existence of men of intellectual distinction.

The permanent ice may be estimated as existing unmelted by the arctic summers, on a circle of about 2000 miles in diameter, of which the North Pole is the centre. This desert of ice extends from the Pole on all sides, for about an average of 15 degrees, or to about the 75th degree of latitude. Explorers have seldom approached, and scarcely in any instance have penetrated, beyond the 74th, except at one portion of the arctic, the North Atlantic, where a southern current, alluded to in a former chapter, has enabled them in one or two instances to pass the 80th degree, and to give the northern outline of Spitzbergen.

For the first 15 degrees, or more than 1000 miles, the earth may be said to be not only uninhabited and uninhabitable, but an unexplored desert of ice; for the second 15 degrees, or another 1000 miles, man exists under such an unfavorable climate, that it appears to have produced no men of any remarkable intellect.

The following table will aid us in illustrating this part of our subject.