[1][2] His father, Theodore Erasmus Hilgard, was for many years Chief Justice of the Court of Appeals, but on account of his liberal opinions was so dissatisfied with conditions in his native country that in 1835 he emigrated to America.

Soon, however, Professor Bache, recognizing his abilities, procured young Hilgard a position in the United States Coast Survey, in which service he continued, with short interruptions, until his death.

In the field work, in computations and investigations in the office, in the publication of the records and results of the Survey, in his influence on political leaders, Mr. Hilgard rendered highly intelligent and valuable aid to the service.

During the failing health of Professor Bache, Hilgard, who was at that time the in charge of the U.S. Coast Survey office, was obliged to perform the duties of superintendent, which he did without extra compensation until the appointment of Benjamin Peirce to the position.

Declining this, but continuing his connection with the International Committee, a beautiful Sèvres vase was presented to him by President Theirs on behalf of the French Government in recognition of his services.

The significance of self-recording magnetometers, as they relate to geomagnetic storms was not fully understood until the late twentieth century and is not referenced in any of the nineteenth-century biographies of Hilgard.