A Brief History of Geomagnetism and a Catalog of the Collections of the National Museum of American History. A Brief History of Geomagnetism and a Catalog of the Collections of the National Museum of American History. Copy, in the Smithsonian Institution, of an original in the Museum of the History- of Science, Cambridge University.).
Lloyd's adaptation of the dip circle to measure intensity by a static method was a vertical force magnetometer. The possibility that the difficulty lies, at least in part, in the imperfection of the instruments used has naturally been explored. With the end of the Napoleonic wars, H u m b o l d t undertook to support p r o m o t e g o v e r n m e n for observations of earth magnetism.
Petersburg, Moscow, Kazan, Barnoul (at the foot of the Alta Mountains), Nertschinsk (near the border with China), Nicolajeff (Crimea) and Beijing (in "the garden of the Greek monks"). Movement of the magnet induced a current in this circuit which moved a magnetic needle in the observatory. Most of the older instruments in the current collection belong to this supposedly quiet period.
The coastal survey showed a decided preference for instruments of the "Kew (Observatory) type", as manufactured by the firm Dover.
MAGNETOMETER
AI.TAZIMUTH INSTRUMENT
34; Account of the Magnetic Instruments in use and of the manner of observation to be set up in the Magnetic Observatories by H e r Majesty's G o v e r n m e n t . 34;Regarding I m p r o v e m e n t of Appliances for Measurement of the Earth's Magnetic Elements by Electric and Magnetic Methods." TM,. 34;Description of the Magnetic Observatory at the Smithsonian Institution." Smithsonian Institution Annual Report for 1859, pages.
Report of the Committee on Physics, including Meteorology, on the objects of scientific investigation in these subjects. Begins (pp. 1-37) with the Society's formal discussion of the m e t h o d s and instruments to be used at Colonial Observatories.]. Revised directions for the use of the magnetic and meteorological observatories and for the magnetic surveys.
It was also used in the early work of the Carnegie Institution. T he design was generally successful, and these magnetometers were used in the comprehensive magnetic survey of the United States that began in 1899. T he arrangement for deflection is shown on the right, where the telescope is mounted on the same base as the telescope. suspension of the 2.
4 of type 1, a n d is modeled after the c o r r e s p o n d i n g Coast Survey instrument and that of the British India Survey. Its weight, 37.5 lb/17 kg, was second only to that of the first generation of magnetometers designed by the Carnegie's D T M. The most important innovation was the replacement of the immersion circuit with an earth inductor (centre, with its galvanometer to the right) ).
It indicates the direction of the earth's magnetic field by a "null method." That is, when the rotor moves on its axis, but is oriented in some direction as the earth's field, a current is indicated in the galvanometer. T h e r e f t e r it was taken on tours almost every year for decades, and was used in the United States, South America, Africa, and on the sixth voyage of the ship Carnegie. The deflection of the magnetized balance beam is then measured by an optical system visible through the small telescope at the top.
T h o m a s Edelmann of Munich was one of the most prolific designers of magnetic devices at the end of the 19th century. It continuously records the total intensity of the field and the magnitude of directional angles.
He made some of the early instruments of the survey, including this o n e , which appears to have been made while in private business. This type of circle became most common in the United States in the late 19th century, and was commonly known as the Kew-dip circle, regardless of manufacturer. A special mount for a defect magnet is usually installed on the reading mechanism to determine the total intensity by Lloyd's method, in which the position of the needle is compared with and without an adjacent defecting rod.
Dover, usually made his initials with i n s t r u m e n t of his manufacture, although this has not been found on any of the i n s t r u m e n t in the present collection. Hotchkiss, later President of the Michigan College of Mines, this instrument was intended to improve the standard dip circle, especially with respect to sensitivity, for the use of mineral prospectors and economic geologists. It proved to be so superior to Lloyd-Creak's diving rings that it continued to be used on the ship's two-and-a-half-hour cruises, circumnavigating the globe several times.
The ratio between the change caused by a unit field and the original magnetic moment of the magnet is called the induction coefficient of the magnet. This plaster model represents the three-dimensional change in declination by hour of day and month of the year based on data collected by A.D. The raised areas at 1pm throughout the months indicate periods when the needle points west of the average position - the average position is indicated by the circle at the lower left and the curved line at the right.
The most significant daily change in the needle's position occurred in August. The model was made by Ferdinand Engel of the Coast Survey to accompany Bache's report on the results of the magnetic observatory at Girard College in Philadelphia. Requests for special treatment - use of colors, folds, bound covers, etc. - request additional approval from the sponsoring authority on the same form.
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