170 



THE POPULAR SCIENCE MONTHLY. 



armament ; their function in war is to capture the commerce-de- 

 stroyers of the enemy, to act as commerce-destroyers themselves, 

 and to convoy and protect fleets of large and fast merchant ves- 

 sels. To accomplish these purposes great speed is necessary, either 

 to overtake or convoy swift merchantmen ; great endurance or coal 

 supply, to enable them to keep the sea for long periods on the 



path usually frequented 

 by merchant vessels ; and 

 offensive and defensive 

 power sufficient to enable 

 them to successfully re- 

 sist the attacks of vessels 

 of their own class. 



The type next in im- 

 portance and general use- 

 fulness is styled the pro- 

 tected cruiser, or those 

 whose only protection 

 against injury consists of 

 sloping armor decks of 

 varying thickness, in 

 combination with coffer 

 dams filled with water- 

 excluding material and 

 closely divided compart- 

 ments in the region of the 

 line of flotation. The 

 characteristics of this 

 type are not capable of 

 being so clearly defined 

 as those already consid- 

 ered, as they include such 

 widely differing vessels 

 as the triple-screw Co- 

 lumbia of 7,350 tons dis- 

 placement, the Olympia 

 of 5,500 tons, down to 



FIG. 6. BROOKLYN. Midship Section. 



A, air duct; CE, cellulose; C, 0, C, coal; 



P, P, P, passages. 



cruisers of 2,000 and 3,000 

 tons displacement as rep- 

 resented by the Cincinnati and Detroit. Their function is a 

 varied though exceedingly useful one ; some are designed particu- 

 larly for preying upon the commerce of an enemy so as to cripple 

 its resources, the most notable examples being the Columbia of 

 our own and the Blake of the British Navy. 



Speed and endurance are the features emphasized, combined 

 with guns of light caliber for dealing with unarmed vessels ; 



