JOSEPH HENRY, LL.D. 295 



So much of value has been gathered by govern- 

 ment surveys and by voluntary contribution that 

 the institution has sent duplicates to various soci- 

 eties of specimens in geology, mineralogy, botany, 

 zoology, and archaeology, while it has remaining, 

 " boxed up, varieties of art and nature " more than 

 enough to twice fill the halls and galleries of the 

 building. 



The work of Professor Henry grew more and 

 more onerous, but he seemed to leave nothing un- 

 done. For many years he served gratuitously as 

 chairman of the Lighthouse Board. When a sub- 

 stitute was needed for sperm oil, after almost num- 

 berless experiments, he showed that lard oil is the 

 best illuminant, thereby saving the country over 

 one hundred thousand dollars yearly, since 1865. 



During the last twelve years of his life, he de- 

 voted much time to our system of coast fog-signals, 

 making " contributions to the science of acoustics, 

 unquestionably the most important of the cen- 

 tury." 



Observations were made, among other places, at 

 Block Island and Point Judith. The distance be- 

 tween these fog-horns is seventeen miles, and the 

 sound of one can be distinctly heard at the other 

 when the air is quiet and homogeneous ; but if the 

 wind blows from one towards the other, the listener 

 at the station from which the wind blows is un- 

 able to hear the other horn. 



While at work in the Lighthouse Depot, in Staten 

 Island, December, 1877, Henry's right hand became 



