POPULAR MIS CELL AX Y. 



*57 



and from this time, till they arrive at ma- 

 turity, they go on always augmenting the 

 diameter of their stems, but at the same 

 time decreasing in number. It is calculated 

 that, if sixteen hundred trees of four inches 

 in diameter can stand and thrive on an acre 

 of ground, there will not be more than four 

 hundred of them when the trees have grown 

 to eight inches, two hundred when they have 

 reached twelve inches, and between one 

 hundred and one hundred and forty when 

 they have attained sixteen inches in diam- 

 eter. Little is to be done in the earlier 

 stages of a forest's growth except to keep 

 the heads of the most valuable species from 

 being overtopped by those which stand 

 near them: and this can be dore best, not 

 by removing the others, but by cutting off 

 or breaking the. tops ; for it is desirable at 

 this stage, for the sake of the natural prun- 

 ing, to have the trees growing as thickly 

 together as possible. At a later stage, thin- 

 nings can be judiciously arranged so as to 

 pass through the entire forest at intervals 

 of from ten to fifteen years, enabling the 

 whole area to be operated on in turn. In ex- 

 ecuting these, the most difficult of all forest 

 operations, it will be well to remember that 

 the object is to give room to the heads of 

 the trees, and not to their stems ; for the 

 stems will never be too close together as 

 long as the heads have room properly to de- 

 velop themselves. The favoring of the most 

 promising trees, and the removal of the 

 weaker ones, together with the preservation 

 of continuous shade to the surface of the 

 ground, while all the trees have sufficient 

 room to grow, should be the particular ends 

 aimed at. 



A tfew Plan for Armored Vessels. The 



Naval Committee of the United States 

 House of Representatives has given favor- 

 able consideration to a new plan for build- 

 ing armored vessels which has been devised 

 by a retired invalid engineer. The principal 

 armorial application consists of a submerged 

 " turtle-back,'' about four inches thick, and 

 extending from side to side and from stem 

 to stern of the vessel and below the water- 

 line, so arranged that an enemy's shot from 

 any direction can hit it only at a deflecting 

 angle, so as to be thrown off rather than go 

 through. The sides of the vessel above the 



turtle - back are filled in with cotton or 

 cork, in which a breach made by the pas- 

 sage of a ball will be self-closed by the 

 elastic action of the substance. They may, 

 moreover, be shot to pieces without destroy- 

 ing the buoyant power of the ship. The 

 guns are mounted upon heavy, impenetra- 

 ble, centrally arranged, cylindrical armor, 

 which extends to the bottom of the ship, 

 and is there seated on an hydraulic cushion. 

 The breech of the gun is also inclosed in an 

 oval armor, so arranged as to deflect a ball, 

 striking it from any point, in a harmless di- 

 rection. The gun is operated by an hydrau- 

 lic loading apparatus, which is worked by 

 one gunner, and hydraulic buffers are pro- 

 vided to take up the recoil. 



The Timber-Line of Mountains. Mr. 



Henry Gannett, noticing, in " The American 

 Journal of Science," Dr. Rothrock's state- 

 ment that, as a whole, there is little or no 

 increase in the altitude of the timber-line 

 toward the equator in the Western hemi- 

 sphere, south of the forty-first parallel of 

 north latitude, observes that the height of 

 the timber-line is purely a question of tem- 

 perature, and that that is a function of the 

 latitude, the elevation, and the mass, of the 

 country in the neighborhood. A great mass 

 of country, if raised to a considerable height 

 above the sea, carries with it the isother- 

 mals. Therefore, in considering the height 

 of the timber-line, "we must regard the 

 mountain-ranges in connection with the pla- 

 teaus on which they stand, their latitudes, 

 heights, and masses, or what, in a measure, 

 sums up these three, their temperatures, as 

 it is by these that its height is determined." 

 The actual elevation above sea-level of the 

 timber-line in the Cordilleras of North 

 America ranges from six or seven to twelve 

 thousand feet. It is lowest in the Coast 

 and Cascade Ranges of Washington Terri- 

 tory, and rises as we go southward through 

 Oregon and California. On the high Sier- 

 ras of Eastern-Central California, forests 

 grow to 10,000 or 12,000 feet, while the 

 ranges of Southern California do not reach 

 the upper limits of forests Few of the 

 ranges of Nevada reach the timber-line, 

 which varies from the height of 9,000 feet 

 in the northern to probably 11,000 feet in 

 the southern part of the State. In Ari- 



