Terrestrial Magnetism and Atmospheric Electricity Volume 17 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1912 Excerpt: ...the difference is well within the probable error of observation. The results of the observatory comparisons in various positions of the needle with reference to the horizontal circle shows that the material of which the instrument is constructed is free from magnetic impurities. When using this instrument in the field at the stations given in Table I it was found that the needle required rather too frequent rebalancing to overcome the changes of magnetic dip at the different stations occupied. To remedy this inconvenience the point of suspension (agate cup) has since been raised, likewise the ends of the needle have been slightly bent upwards to bring them in line with the suspension point. Figure 3 is a general view of the mounting of the needle and reading microscope used in testing the materials entering into the Table I.--Results of Comparison Observations with Compass Declinometer No. 2. construction of Compass Declinometer No. 2. This testing apparatus consists of a long magnetic needle mounted in a wooden casing upon a pivot. The needle is made of "magnet steel," and is 201.4 mm. in length with a cross-section of 0.3 mm. by 3.2 mm. The wooden casing is mounted on a metal (brass) base provided with three foot screws. On top of the case is mounted a reading microscope containing a graduated glass scale to facilitate the noting of the motion of the needle when tests are being made. The inside dimensions of the wooden case are 206 mm. in length with a cross-section of 8.0 mm. by 3.5 mm. About 10 mm. at each end of the needle casing is made of very thin material to enable The two functions of u, ( ) ancl f (M) contain the chief the test piece to be brought as close as possible to the needle. The test piece can be brought within abou...