PHILOSOPHICAL SOCIETY OF WASHINGTON. 29 



harbor, but was compelled to anchor so thick was the fog ; yet we 

 heard Little Gull though 7i miles off, at a force of 6 in the scale of 

 ten, and the sound was so clear cut and distinct that we could dif- 

 ferentiate it from the siren at the New London light, which was 

 much nearer to us. The steamer worked round to inspect the 

 neighboring lights, and we heard the Little Gull siren when at 

 North Dumpling light station, 7 miles off, at a force of 6 ; at 

 Morgan's Point Light, 10 miles off, at a force of 5, and we contin- 

 ued to hear it at an intensity of from 5 to 6 as we worked around 

 among the other lights, within a compass of 10 miles, till the fog 

 broke* and the siren ceased. 



Opportunity soon occurred for making more critical experiments. 

 •On a fine day we ran out to Little Gull, had the siren started under 

 full steam, and then, following out a pre-arranged program, ran 

 round Little Gull Island in such way, as to describe a rectangle of 

 about 8 by 10 miles, its longest side running nearly north and 

 south. No fixed rate of speed was maintained, but the steamer 

 slowed, backed, or stopped, as was necessary. The atmosphere was 

 what the sailors call lumpy, and Prof. Tyndall calls non -homo- 

 geneous. Prof. Henry, when writing of a like condition, said : 

 *" As the heat of the sun increases during the first part of the day, 

 the temperature of the land rises above that of the sea, and this 

 excess of the temperature produces upward currents of air, disturbing 

 the general flow of wind, both at the surface of the sea and at an 

 elevation above." Observations were made and noted in a scale of 

 ten, of the force or intensity of the signal's sound as it reached us 

 at the end of each minute. The following Table D shows a sufficient 

 number of the results for our purposes, taken from the tabulated 

 schedule of our notes. The table also shows the condition of the 

 atmosphere during our observations. 



*L. H. Board's Rep. for 1875, page 116. 



