ROYAL SOCIETY OF LONDON
Series A. Mathematical and Physical Sciences N0.818 Vol.240 pp. 251-294 29 April 1947
THE EARTH'S MAGNETIC FIELD IN SOUTHERN AFRICA AT THE EPOCH, 1 JULY 1930
E. N. GRINDLEY
Printed and published for the Royal Society
By the Cambridge University Press
Bentley House, N.W.1
UNIVERSITY OF CAPE TOWN
(WITH WHICH IS INCORPORATED THE SOUTH AFRICAN COLLEGE)
Department of Physics University of Cape Town, Rondebosch, Cape Town. Republic of South Africa.
15th April, 1969.
Professor I.V. Toroptsev,
Rector of the Tomsk Medical Institute,
Moscovsky Tract 2,
TOMSK. U. S. S. R.
Dear Professor Toroptsev,
I have been asked to reply to your letter of September 30th 1968 in which you ask for data in terrestrial magnetism measured by Professor J.C. Beattie in the summer of 1908, as I am more familiar with his work than the other members of our University staff.
During the years 1898 to 1915 he made magnetic measurements at more than 600 places in South Africa, South West Africa, Bechuanaland and Rhodesia. The results for about 400 of these "stations", (up to the year 1906), are given in a large book entitled "Report of a Magnetic Survey of South Africa", published in 1909 by the Royal Society of London. His later work appeared in various periodicals, chiefly the Transactions of the Royal Society of South Africa.
I think it will be difficult to obtain copies of these publications, as they were all printed more than 50 years ago, but I am sending you a reprint of a paper in which I have made use of the work of Beattie and a number of other observers who have made similar measurements in this part of Africa.
Table 2, which starts on page 275 contains a list of all the "stations" occupied by various observers (including myself in the years 1928 to 1930), and shows the original values of the magnetic field as measured by these observers, and the dates to which these values refer. Beattie's values given in the "Report" were all "corrected to Epoch 1903.50", (that is, the probable value at the middle of 1903 were 1903 were calculated). A number of Beattie's later values were corrected to epoch 1908.50. The other dates given (in the 7th column of the table) are the actual dates of observation.
In the 4th column of the table, the numerals show the source of the original observations; 1, 3, 4, 5, 6, 7 and 9 denote work by Beattie or his partner, Professor Morrison.
Beattie's apparatus was a magnetometer of the Kew pattern for measuring magnetic declination and horizontal intensity, a Dover "dip circle" for measuring the magnetic inclination, and a Cooke theodolite with a 12.5 cm circle for making the sun observations for finding "true North".
The instrumental errors on the magnetometer were small -probably less than 11 (one minute of arc). Values for the horizontal intensity obtained by using the deflecting magnet at two different distances usually agreed to better than 10 V (.00010 gauss or oersteds). Errors in the inclination are more difficult to estimate. Four different needles were used, and their direction of magnetization was reversed, but the values obtained with different needles usually differed by 2' or 3 '. (Observations were made to the nearest 0.1').
Attempts were made to allow for the effect of diurnal variation (range about 10' in declination on "quiet" days), but as there was then no magnetic observatory in South Africa the effect of "high" days and "low" days could not be estimated. (Most stations were only occupied for one day) .
If you are particularly interested in the observations taken in the year 1908, they are those marked 4 in the 4th column of the table.
I hope this information will be useful to you. If you wish for further details, I shall be happy to try to find them for you.
Dr. E.N. Grindley
Retired Lecturer in Physics