MAURITIUS AND CHRISTCHUKCH TERM-HOUR RECORDS. 147 



The copies of the Mauritius curves sent by Mr. CLAXTON were traced by Mr. BROOKES with the curve- 

 tracer designed by Dr. AD. SCHMIDT, and the results from the different term hours were arranged so as to 

 appear in juxtaposition. 



47. In Plate I the successive curves appear one below the other so as to have a common time scale ; 

 the vertical cross lines answer to 10, 20 ... 60 minutes from the commencement of the term hour. The 

 date and the term hour e.g. 6-7 a.m. on May 1, 1902 appear on the left-hand margin. This also 

 shows the absolute value of the Horizontal Force at the commencement of the term hour, as given by 

 Mr. CLAXTON'S own measurements (r,f. the table on p. 174 of "Physical Observations"). The scale value 

 (1 mm. = 2'93y, or 20y = 7 mm. approx.) is also shown at the side. Motion down the sheet means 

 increase of force, as is indicated by the arrows. 



On May 1 and June 1 the trace was lacking for a few minutes at the commencement of the hour. 



At Mauritius the drums, when quick run, were rotated at twelve times the usual rate. Normally the 

 time scale is about 15 mm. to an hour, and so in the quick-run curves it is about 186 mm. to the hour. 

 Plate I shows the curves natural size. 



To the eye the departure of the curves from straight lines is not very conspicuous. It is, in fact, so 

 small that it was deemed inexpedient to draw horizontal lines across the sheet to show the absolute 

 values. If anyone wishes to measure variations in the ordinate he may employ as base line the time line 

 at the top. The absolute value of this for the curve of any one hour can be readily arrived at by reference 

 to the absolute value assigned to the commencement of the hour in question. 



Plate II gives the slow-run Mauritius Horizontal-Force curves for the remaining term hours for which 

 records were available. To show the trend of the curve, the record extends for about 20 minutes on 

 either side of the term hour, except on October 1, when the original record stopped immediately after the 

 end of the hour. On April 15, 1902, and February 15, 1903, there were small gaps in the original, 

 representing probably the interval required to change the photographic paper on the drum. The curves 

 in Plate II are all very quiet, but owing to the small time scale they appear less quiet to the eye than the 

 quick-run curves in Plate I. On February 1, 1902, there was quite an appreciable amount of variation, 

 but this unfortunately was prior to the arrival of the " Discovery " at Winter Quarters. The curves of 

 October 15, 1902, and January 1, 1903, show some small oscillations. 



The original curves had, of course, separate base lines having different absolute values. To economise 

 space, the curves have been so placed in Plate II that a common base line serves for all in one horizontal 

 row. There are thus only three base lines shown, the top one serving for the term hours of the four days 

 February 1 and 15, and March 1 and 15, 1902. In addition to the base line for each group of curves 

 there is a second straight horizontal line, answering to a value of the force exceeding that for the base line 

 by 50y. As in the case of the quick runs, the curves are as nearly as possible exact copies of the original, 

 1 mm. of ordinate representing 2 - 93y. As indicating the truly remarkable absence of disturbance, it may 

 be remarked that there is not one of the curves reproduced which shows a range exceeding 6y during the 

 term hour. 



48. At Christchurch, as already stated, quick-run traces were available not merely for the term hours, 

 but for the term days. It was decided, however, for reasons subsequently stated (App. A), to reproduce 

 only two specimens of the term-hour records, and to deal with the Christchurch tabulations in a special 

 Appendix. 



The curves selected for reproduction were those taken during the term hours of June 15 and July 1, 

 1902. Their selection was due to the fact that on these days there were corresponding quick-run curves 

 from the Antarctic. 



The Christchurch curves for the term hours of June 15 and July 1 appear in Plate III. To economise 

 space, a single time or base line is drawn to serve for the three elements from each hour. The Declination, 

 Horizontal-Force, and Vertical-Force traces are distinguished by the letters D, H, and V respectively. 

 The absolute value of each element at the commencement of the hour and the corresponding scale value 

 are shown at the left margin. The arrows assist in indicating the direction in which the elements increase 

 (at Christchurch, down the sheet answers in all the elements to an increase). The curves in the 

 photographic copies sent from Christchurch were copied by Mr. BROOKES with the Schmidt tracer. The 



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