EESE ARCHES IN SOUND. 551 



45*^ to the riglit of tlie direction of the wind, and after proceeding about 

 one mile, as estimated by time, we lost the sound of the signal. ATe 

 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 direc- 

 tion of the wind and the axis of the trumpet combined. From this point 

 it was heard to a point to the leeward, and thence we retraced our 

 course at about the same distance and proceeded a<jross the axis of the 

 trumpet toward the wind\7ard, where the sound was again lost. The 

 only definite result from this experiment was another case of the sound 

 being heard farther to the leeward than to the windward. 



After this experiment we rptumed to Portland. 



An interesting fact may be mentioned in connection with this station, 

 having a bearing upon the i^rotection 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, desir- 

 ing to connect the light-house and fog-signal by an electrical communi- 

 cation, susi)ended a wire between the two points and attempted to form 

 a ground connection by depositing a plate of metal in the ground on 

 each island, but to his surjjrise, though the arrangements were made by 

 a skilled telegrapher, no signal would pass. The two islands being- 

 composed of rock and the soil limited in thickness, the conduction was 

 imperfect, and it was only by plunging the plate of metal into the water 

 on each side of the space between the two islands that a signal could 

 be transmitted. 



No further experiments on sound were made during this excursion, 

 because the vessel could no longer be spared from more pressing light- 

 house duty in the way of inspection and the stated supply of mat<3rials 

 to the stations. 



On my return to New York, accompanied by Mr.NWoodrufP, I took the 

 route by the Western Railway to the Hudson Eiver at Troj'. This line 

 was chosen in order to make some investigations relative to any pecu- 

 liarities of sound which might be observed in the Hoosac tunnel, through 

 which the railroad passes. For this purpose we spent a day at East 

 Windsor, a village situated near the west end of the tunnel, and were 

 very cordially received by the engineers in charge. 



The tunnel is four and three-quarters miles in length, twenty-four feet 

 wide, and twenty feet high to the crown of the arclu It ascends slightly 

 from either end to a i)oint near the center, where there is a veutUating- 

 shaft 1,028 feet high extending to the outer air above. In winter, when 

 the external temperature is less than thgit within the tunnel, there is a 

 constant current from each end toward the center, and in the summer, 

 when the temperatures are reversed, there is a current out of the tunnel 

 at either end, except when the external wind is suflBciently strong, es- 

 pecially from the west, to reverse the direction of the cuiTent from one 



