412 WRITINGS OF JOSEPH HENRY. [1874 



In arranging the signal the hell and machinery must he placed as low as 



Eossihle, as the sound is heard much more plainly on the water when the 

 ell is near its surface, and also as the machinery, when thus situated, is 

 steadier and more readily accessible. 



Particulars as to the siren. — The boiler of a second-class apparatus is 12 

 feet long, 42 inches in diameter, and has 300 feet of heating surface. The 

 dome is 2 feet in diameter and 3 feet high. 



The cylinder of the engine is 4 inches in diameter and 6 inches stroke. 

 The prolongation of the piston-rod forms the plunger of the feed-pump. 

 The main shaft carries three pullej's ; the larger driving the siren-spindle, 

 the second, the worm and screw-gear, and the third, the governor. 



In the worm-gear the wheel makes two revolutions per minute, and is 

 provided with a cam, which acting on a lever opens the valve, admitting 

 steam through the siren-disks. The cam has such a length as to hold the 

 valve open for about seven seconds. A counter-weight closes the valve a9 

 soon as the lever is released by the cam. 



The siren itself consists of a cylindrical steam-chest, closed at one end by 

 a perforated brass plate. The perforations are twelve in number, equi-distant 

 from each other, and arranged on the circumference of a circle, whose center 

 is in the axis of the cylinder. The other end is closed by a cast-iron head. 

 The heads are connected by a brass pipe, through which the spindle passes. 



The perforated head is covered on the exterior by a brass disk, attached to 

 the spindle, having twelve rectangular notches corresponding to the aper- 

 tures on the former, and so arranged that by its revolution these apertures 

 are simultaneously opened and closed. The spindle is driven by a belt from 

 the large pullej^ on the main shaft. This shaft makes 180 revolutions per 

 minute; the spindle, 1,620 ; and as there are 12 apertures in the disks, from 

 each there will issue jets of steam at the rate of 19,440 per minute. The 

 sound produced by these impulses may be rendered more or less acute by 

 increasing or diminishing the velocity of revolution. 



The valve and valve-seat are disks similar to those already described, hav- 

 ing however four openings instead of twelve. The valve revolves on the 

 brass tube inclosing the siren-.spindle, and is worked by a bevel gear. The 

 trumpet is of cast-iron. 



The Daboll trumpet. — The apparatus used in the foregoing experiments is a 

 second-class trumpet, operated by an Ericsson caloric-engine. The air-pump 

 is single-acting. Its cylinder is 12 ins. in diameter by 12 in. stroke. The 

 engine makes 40 strokes per minute. There is a screw-thread raised on the 

 main shaft, which acting on a wheel drives a bevel gear, giving motion to 

 a cam-wheel. The latter makes one revolution in two minutes, and is fur- 

 nished with three equidistant cams. These cams — pressing on the valve- 

 lever, throw the valve open once in forty seconds, admitting the compressed 

 air through the reed-chest into the trumpet. 



The quantity of air forced into the tank should be in excess of that needed 

 for the trumpet, the surplus being allowed to escape through a delicate safety- 

 valve. This is necessary to provide against a deficiency in case of leakage, 

 and also to allow the pressure of air to be regulated to accommodate the 

 reed. Each reed requiring a different pressure, it is necessary to alter the 

 pressure of the valve-spring whenever a reed is changed. 



The first-class trumpet diflfers only in size from that described. 



The caloric-engine for the first class has a 30 in. cylinder. The air-pump 

 is IGi ins. by 15 in. stroke. 



The steam-whistle. — The boiler of this machine is that of the siren. On 

 the forward part of the boiler, the bed-plate of a small engine is secured by 

 two cast-iron brackets. The cylinder of this engine is 4 ins. by 9 ins. The 

 fly-wheel shaft carries an eccentric, which, acting through a rod and pawl on 

 a ratchet-wheel, gives the required motion to the cam-wheel shaft. 



The cam-wheel (which makes one revolution per minute,) is provided with 



