490 WRITINGS OF JOSEPH HENRY. [1877 



the loudness. Two sounds may be equally loud whwi heard 

 near by, yet differ very much in regard to their being heard 

 at a distance, the loudness depending upon the intensity of 

 sound or on the amplitude of vibration of the sounding 

 body, while the quantity of sound depends on the extent of 

 the vibrating surface. 



The size of the whistle must be limited by the quantity of 

 air ejected at each oscillation of the buoy. The fact that 

 the ten-inch whistle gives a sound which can be heard far- 

 ther than one of eight inches, appears to have a bearing on 

 the question of the united effect (the actuating force being 

 the same) of two sounds of the same quantity and pitch, 

 since the sound from several parts of the circumference of 

 the larger whistle may be considered as a union of several 

 sounds of less quantity. 



Whitehead Station. — After these observations on the auto- 

 matic buoy we proceeded along the coast to Whitehead, at 

 the entrance of Penobscot Bay, a distance of sixty miles, 

 which we reached at about twelve o'clock at night, and cast 

 anchor in Seal Harbor, near the Whitehead light-house. 



Our first operation next morning was the examination of 

 an automatic fog-bell, invented by Mr. Close, and which has 

 been erected by a special appropriation of Congress. It is 

 ver}'^ simple in conception, and would do good service in 

 southern latitudes, where it would not be affected by the ice. 

 It consists of an upright shaft thirty-two feet long, fastened 

 to the rock beneath the water and kept in a vertical position 

 by a series of iron rods serving as braces. Around this shaft 

 is a hollow metallic float, having sufficient buoyancy to ele- 

 vate a vertical rod by the motion of the waves, having at the 

 upper end a rack gearing into a ratchet-wheel. By means 

 of projecting pins on the surface of the wheel, the hammer 

 of the bell is elevated and the bell sounded at each descent 

 of the float. This arrangement is the most simple and 

 efficient of the kind of which we have any knowledge. 



The objection to it is its liability to be deranged by the 

 action of ice and the rusting of the parts from exposure to 

 the weather. 



