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spark from the magnetism of the earth. This consists in the rapid 
revolution of a large bar of soft iron on a horizontal axis at right 
angles to its length, in the plane of the meridian, the bar being 
surrounded with a very long wire insulated with a covering of silk, 
an arrangement being made to break the circuit at the instant of 
the bar receiving the greatest amount of magnetic induction. He 
succeeded, by this arrangement, in producing currents of electricity 
of considerable power, but for the want at the time of a sufficient 
length of insulated wire, he was unable to increase the intensity suffi- 
ciently to produce the spark.’’ * 
Although Saxton’s preéminent ability as a mechanician had se- 
cured for him the tender of the office of director of the printing 
machinery of the Bank of England, he preferred to return to the 
United Siates and to accept the office of constructor and curator of 
the standard weighing apparatus of the Philadelphia Mint. During 
his connection with the Mint he constructed ‘‘ the large standard 
balances still used in the annual inspection of the assays and the 
verification of the standard weights for all the Government assay 
and coining offices in the United States. The knife edges of these 
implements are of the hardest steel, turning upon plates of agate ; 
and such sensibility has the apparatus that when loaded with fifty 
pounds it turns with one-tenth of a grain; or, in other words, with 
the three-millionth part of its load.’’ 
Already, in 1834, he had been awarded the John Scott medal of 
the Franklin Institute for a reflecting pyrometer, in which he had 
utilized the mirror method of observation to determine the temper- 
ature by means of the linear expansion of a metallic rod when 
under the influence of heat. In 1843, upon his appointment by 
Professor A. D. Bache to the office of Superintendent of Weights and 
Measures, he applied this mirror method to the construction of the 
standard bars used by the Coast Survey in such a way as to secure 
an unvariable length in the bar when subjected to different temper- 
atures. This was done so successfully that the different measure- 
ments of a base line five miles in length did not differ by more 
than half an inch. 
In 1858, Saxton presented to the American Association for the 
Advancement of Science, at its Baltimore meeting, a paper giving 
an account of the principal applications which he had made of the 
* Henry’s Biographical Memoir, loc. cit., p. 303. 
