| The Dip Needle is a compass pivoted to move
in the plane containing the magnetic field vector of the earth. It will then
show the angle which the magnetic field makes with the vertical.
The needle must be accurately balanced so that only magnetic torques are exerted on it. Some texts suggest that the dip angle be measured twice, with the poles of the needle reversed by remagetization between trials, and the results averaged. Some instruments allow the needle and circle to be rotated to allow use as a compass.
The Miami apparatus was made by W. & J. George of London and Birmingham.
|This dip needle was made by Ferdinand Ernicke of Berlin, and was on display at the University of Colorado physics department in 1975 when this picture was taken.|
| The dip needle (or inclination compass) at
the left was purchased from Ruhmkorff of Paris, probably in 1875, for Vanderbilt
University. It is now on display in the Garland Collection of Classical
Physics Apparatus at Vanderbilt.
"In carrying out a measurement one sets the needle in the magnetic meridian by turning the support until the needle is vertical, in which case the needle is in a magnetic East-West plane, and then turns the support exactly 90°, at which point the vertical scale circling the needle is in the magnetic meridian. Thereupon the angle the needle makes with the horizontal is the angle of inclination. ... The horizontal circular scale is marked off in half degrees. The associated vernier allows readings to one minute. The vertical scale is marked off in ten-minute intervals." (From Robert A. Lagemann, The Garland Collection of Classical Physics Apparatus at Vanderbilt University (Folio Publishers, Nashville, TN, 1983) pg 152)
The instrument at the left appears to be exactly the same as the one above it. However, it is marked "Gambey à Paris".
It is in the apparatus collection of Case Western Reserve Unversity in Cleveland, Ohio.
This Phelps and Gurley (Troy, New York) dip needle was bought by Dartmouth College in 1862. With its case and extra needle it was valued at $20.00.
Attached to this apparatus when I looked at in June
2001 was the following information: " Provided it is well removed from local
influences such as iron, magnetite and other ferromagnetic materials, a
compass needle that is free to rotate in a vertical plane will point downward
in the northern hemisphere at an angle from the horizontal along the line
of the Earth's magnetic field. The instrument for measuring this angle is
called an inclinometer, dip needle or, most frequently, dip circle."
|| The dip needle at the left is on display at the University
Museum at the University of Mississippi in Oxford. The mechanism pivots
so that it can be used either as a dip needle, or, in the horizontal orientation,
as a compass.
The accompanying placard identifies it as being made
by Lerebours et Secretan of Paris, but it is not in the 1853 L&S catalogue
where so much of the apparatus purchased by Frederick A.P. Barnard in the
second half of the 1850s can be found.
| The dip needle at the right is at the department of physics
at the University of Texas at Austin.
The 1888 Queen catalogue lists it as "Inclination
Compass. Vertical circle, ten inches in diameter, horizontal circle, five
inches; brass posts, base and leveling screws, all delicately finished ...
This dip needle is at Westminster College in New Wilmington, Pennsylvania. It is about 30 cm high and has no maker's name.
It can be flipped horisontally for use as a compass.