6i8 THE POPULAR SCIENCE MONTHLY. 



termination between the observatories at Paris and Greenwich, which 

 supersedes the A'alue previously admitted, correcting it by nearly 

 half a second of time. His essay on " Tides and Tidal Action in Har- 

 bors," first jDublished as a lecture before the American Institute, is re- 

 markable for its lucid and terse exposition of principles without the 

 aid of mathematical symbols. While possessing great facility in em- 

 ploying the aid of the higher mathematics, Mr. Hilgard systematically 

 avoids, as far as practicable, their introduction in his writings, j^refer- 

 ring to use logical statements of the processes of reasoning. 



As part of the duties of his office, Mr. Hilgard has charge of the 

 construction and verification of the standards of weight and measure 

 for the United States, and, by order of Congress, has been for some 

 years past engaged in preparing metrical standards of great precision 

 for distribution to the several States. In this connection he was ap- 

 pointed a delegate to tlie International Metrical Commission, which 

 met at Paris in 1872, having for its object the construction of new 

 metrical prototypes of great precision and permanence, and which 

 has since resulted in the establishment of an International Bureau of 

 Weights and Measui-es at Paris, under the direction of a committee, 

 of which Mr. Hilgard is a member. A valuable and instructive trea- 

 tise on " Methods of Precision in measuring and weighing " was read 

 by him before the Stevens Institute of Technology, but has not yet 

 been published. 



When, in 1863, the National Academy of Sciences was chartered 

 by Congress, Mr. Hilgard was one of the original members named in 

 the act. He is at present the home secretary of that scientific body. 

 The compliment of honorary membership has been conferred upon him 

 by the American Philosophical Society of Philadelphia, and the Acad- 

 emy of Arts and Sciences of Boston. His frequent communications 

 to the Philosophical Society of Washington are evidence of a very 

 active interest in scientific research, maintained notwithstanding the 

 exactions of his arduous official labors. A work of great interest, 

 which he is now conducting outside of his official sphere, is a mag- 

 netic survey of the United States, prosecuted at the expense of the 

 Bache Fund, arising from a bequest of the late Alexander Dallas 

 Bache to the National Academy of Sciences. 



No small part of Mr. Hilgard's services to science and education is 

 to be found in the readiness and obliging disposition with which he 

 has constantly given information and rendered facilities by the loan 

 of instruments and apparatus to persons engaged in scieutitic research 

 or instruction. Besides meeting numerous requests of this kind at 

 home, he has given his best aid and advice to the equipment of gov- 

 ernment surveys in the SandAvich Islands and in Japan. Although Mr. 

 Hilgard's scientific work has been generally limited to the sjjhere em-, 

 braced in his practical pursuits, he has been a very active student in 

 other branches of science, especially dynamics and molecular physics. 



