498 WRITINGS OF JOSEPH HENRY. [1877 



first, second, and third experiments were made on the day 

 before. The wind had changed about four points to the south- 

 ward. As in the preceding experiments, the sound was lost 

 again at the distance of about one-fourth of a mile, but was 

 not distinctly regained, though some of the observers thought 

 they heard it at a distance of two and one-half miles. 



The only perceptible difference in the wind (on the 5th) 

 was that it was a little less rapid, and four points more to 

 the southward. 



From a subsequent report of the keepers, the whistle of 

 the vessel was heard continuously as far as the puffs of steam 

 could be observed — a distance of six or seven miles. In this 

 case the sound was moving with the wind. These results 

 therefore are in accordance with those previously obtained. 



Monhegan island. — The next experiments were made at 

 Monhegan, an island sixteen miles south-west of Whitehead. 

 On this island there is a Daboll trumpet actuated by a hot- 

 air engine. 



We departed from this station in a westerly direction at an 

 angle of 45° to the right of the direction of the wind, and after 

 proceeding about one mile, as estimated by time, we lost the 

 sound of the signal. We then turned at right angles to our 

 former course and proceeded toward the leeward, keeping 

 about the same distance from the signal, when the sound 

 was regained at a point which probably depended upon the 

 direction of the wind and the axis of the trumpet combined. 

 From this point it was heard to a point at the leeward, and 

 thence we retraced our course at about the same distance 

 and proceeded across the axis of the trumpet toward the 

 windward, where the sound was again lost. The only defi- 

 nite result from this experiment was another case of the 

 sound being heard farther to leeward than to the windward. 



After this experiment we returned to Portland. 



An interesting fact may be mentioned in connection with 

 this station, having a bearing upon the protection of light- 

 houses from lightning. The fog-signal is placed on a small 

 island separated from the large island by a water-space of 

 about one-eighth of a mile. General Duane, desiring to 



