316 BULLETIN OF THE 



Service on the Light-house Board. — While the whole high 

 bent of Henry's mind was rather toward abstract than utilitarian 

 research, there was no well devised system of practical benefit 

 for man, that did not command his earnest sympathy or enlist 

 his active co-operation : — no labor in such co-operation from 

 which he shrank, if he felt that without the sacrifice of other 

 duties, he could make such labor useful. On the establishment 

 of the Light-house Board, in 1852, Henry was appointed as one 

 of its members ; and although his valuable time was already 

 fully occupied, he consented to serve on the Board, in the hope 

 of aiding to benefit the interests of navigation. To the require- 

 ments of his new position, he brought his accustomed energ}^ 

 skill, and eminently practical judgment ; and soon made his 

 influence felt throughout the Light-house service. 



"When the steadily advancing cost of whale oil made it neces- 

 sary to seek for some more economical illuminant, he attacked 

 the problem with bis habit of scientific method. Colza oil or 

 rape-seed oil had been used in France with some success ; and 

 efforts were made to introduce its culture and production in this 

 country. Lard-oil had been tested by Professor J. H. Alexander 

 of Baltimore, and pronounced by him of very inferior value as an 

 illuminant. For accuracy of determination, Henry caused to be 

 prepared at the Light-house Depot on Staten Island, a long 

 dark fire-proof chamber, and had it painted black on all its 

 interior surfaces for the purpose of photometric observations. 

 In ordinary lamps, the colza oil was found to be nearly equal to 

 whale oil in illuminating power, and lard-oil inferior to it. Pe- 

 troleum or mineral oil was also tried ; but its quality was at 

 that time too variable, and its use was found to be too dangerous. 

 Experiment showed that lard-oil had a greater specific gravity 

 than sperm oil, a less capillarity or ascensional attraction in a 

 wick, and a less perfect fluidity. The conditions were varied; 

 and it was found that with elevation of temperature, the fluidity, 

 and the capillarity, of the lard-oil increased more rapidly than 

 those of the sperm oil, until at about 250^ F. the former sur- 

 passed the latter in these qualities. With these results, it became 

 important to compare the oils in large lamps, such as were actually 

 required for the lanterns of light-houses. The heat evolved by 

 the large sized Argand burners, would seem peculiarly to favor 

 the lard-oil : a few trials, with a proper adaptation of the lamps, 

 established its supremacy; and conclusively demonstrated — con- 

 trary to all the laboratory trials of former experimenters, that for 

 the purpose desired, this contemned article was for equal quan- 

 tities a more brilliant illuminant than mineral kerosene-oil, or 

 vegetable colza-oil, or animal sperm-oil, while its market price 

 was only about one-fourth that of the latter. Against all the 

 opposition of interested dealers, and prejudiced keepers, the lard- 



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