1877] WRITINGS OF JOSEPH HENRY. 499 



connect the light-house and fog-signal by an electrical com- 

 munication, suspended 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 surprise, — 

 though the arrangements were made by a skilled telegra- 

 pher, no signal would pass. The two islands being com- 

 posed of rock and the soil limited in thickness, the conduc- 

 tion 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 

 transportation of the stated supply of materials to the sta- 

 tions. 



On my return to New York, accompanied by Mr. Wood- 

 ruff, I took the route by the Western railway to the Hudson 

 River at Troy. This line was chosen in order to make some 

 investigations relative to any peculiarities 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 arch. It ascends slightly from either end to a point 

 near the centre, where there is a ventilating shaft 1,028 feet 

 high extending to the outer air above. In winter, when 

 the external temperature is less than that within the tunnel, 

 there is a constant current from each end toward the centre, 

 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 sufficiently strong (especially from 

 the west) to reverse the direction of the current from one 

 half, and direct the stream entirely out of the other entrance. 

 At the time of our visit, there was a gentle current flowing 

 out of both ends. 



The only peculiarity of sound which had been observed 



