108 NAVAL SCIENCES. 



also stocks (pi SI, fig. 5), on which new ships are built. These are after- 

 wards covered over with an arched roof, which protects them from the 

 weather. Fig. 3 shows a crane for setting masts. This machine is some- 

 times movable, and in that case placed on a scow. Fig, 4 shows a pile- 

 driving machine, for the purpose of driving posts and pile-bottoms into 

 different places in the harbor. 



E. Arsenals. 



Navy yards, or harbors for men of war, always have an arsenal, where 

 the equipments of ships are kept and also manufactured. Here are found 

 cannons, balls, bombs, anchors, and so forth. There are also a forge for 

 anchors, a cannon foundry, an iron foundry, a rope walk, a sail-maker's loft, 

 and in short, all the mechanics' shops in which the utensils of a ship are 

 made. 



F. Diving Bells. 



A very useful apparatus, the diving bell, is also kept in harbors and road- 

 steads. It is well known that when a bell is immersed in the water, the 

 presence of the air inside counteracts the power of the water, so that 

 if the bell is of sufficient size, one or more men can descend in it to the 

 bottom of the sea, and there pursue their labors (pi. 30, fig. 6). For this 

 purpose, a frame with a strong tackle is fitted on a boat, by which the bell 

 is suspended. This is then let down with men in it, who remain at the 

 bottom until they give a signal to be drawn up. They take ropes and 

 chains with them, which are attached to any object which they wish to save 

 and this is drawn up together with the bell (fig. 1). In order to supply 

 the men with fresh air, leather hose pass to the surface of the water, pro- 

 vided with valves. Bv means of them the bad air is discharged, and fresh 

 air supplied. 



G. Observatories. 



Observatories, with signal-lights for night use, are erected for the purpose 

 of seeing ships as they come into the harbor, and of noticing everything 

 which may occur on the water and of reporting arrivals by signals (pi. 4, 

 fig. 8). PI. 31, fig. 2, and pi. 30, in the lower corner at the right, show 

 several of these observatories. 



H. Light-Houses. 



Many dangerous points are found on coasts, where sailors who are 

 not acquainted with the locality, or who have no pilot on board to take 

 them over the dangerous places, are very liable to suffer shipwreck. These 

 points are designated by signals. High towers are erected, in which lights 

 are kept burning all night. Light-houses are also built at the entrance of 

 harbors (pi. ^,fig- 6). In the earlier ages, fires were made use of as signals ; 

 but at the present day, lamps, provided with reflecting apparatus on a large 

 scale, are employed. As this light might be easily mistaken for a star, they 

 are so arranged that the light is shown only at intervals, or periodically 

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