1875] WRITINGS OF JOSEPH HENRY. 455 



at several hundred feet on either side of it. The interval 

 between the cessation of the original sound and the com- 

 mencement of the echo was not as marked as in some 

 previous observations, not being more than four or five sec- 

 onds. The duration of the echo was on the average about 

 eight seconds, — beginning with the time of its first perception 

 and not with the cessation of the sound of the trumpet. 

 General Woodruff and Dr. Welling both noted the peculiar 

 character of the echo, which was that of a series of reflections 

 varying in intensity from a maximum, near the beginning, 

 and gradually dying away. The wind was nearl}'' at right 

 angles to the axis of the trumpet and also to that of the 

 crests of the swell of the ocean, which was rolling in from 

 the effects of a distant commotion. The barometer at 12 m. 

 indicated 30"2 inches; the dry-bulb thermometer 73° F., the 

 wet-bulb 70° F., indicating a remarkable degree of aqueous 

 saturation. During the whole day the air in all the region 

 around Block Island was undoubtedly in a homogeneous 

 condition. 



August 6, 1875. — On this day tlie weather was nearly the 

 same. The fog-signal on the 5th instant was kept in opera- 

 tion for the use of the mariner nineteen hours, and on this 

 day it was blown twenty hours continuously. The barometer 

 marked 30'2 inches; the thermometer 70° F. ; the fog not 

 as equally distributed as on the preceding day; the north 

 end of the island (distant four miles) being distinctl}^ visible. 

 The wind was S. W. to S., making an angle of about 60° 

 with the axis of the fog-trumpet. The echo continued to be 

 heard distinctly with a sound varying in intensity, bat was 

 not so loud as we have heard it on certain occasions in pre- 

 vious years. 



During this and the preceding day workmen were em- 

 ployed under Mr. Brown in inserting a flexible India-rubber 

 tube two inches in diameter between the revolving plate of 

 the siren and the smaller end of the trumpet, so that it might 

 be brought into a vertical position. This work — though 

 apparently simple, was difficult in execution, since it in- 

 volved the necessity of strong supports for the cast-iron 



