252 Reports on Special Researches 



DccUnation. Dr. F. Linke, in a letter dated Gottingen, January 6, 1908, stated that 

 the Tesdorpf magnetometer No. 197.5, used at the Samoa Observatorj' in 1906, gave a 

 vahie of west magnetic declination at Potsdam 0'.74 higher than that obtained with the 

 Potsdam standard. Hence, since we regard west decHnation as negative: 



(n) Potsdam -Tesdorpf No. 1975=+0'.74 (Linke, 1907). 



From the CI. W. comparisons at Samoa in 1906 (Table 2.3 A, p. 257) it was found from 

 2 sets: 



(6) C. I. W.-Tesdorpf No. 1975= +1'.10 (C. I. W. 1906). 



Combining (a) and (h) we get: 

 (c) C. I. W.- Potsdam = +0'.36 (1906-07), 



which is in good agreement with the value (+0'..34) found above in Table 20 A. 



Horizontal hUcnsily. According to //-comparisons made by Dr. Linke in October and 

 November 1904, between Tesdorpf magnetometer No. 1975 and the standards at Potsdam 

 and Cheltenham, it was found that with the relative constants for No. 1975 as determined 

 at Potsdam,' (Potsdam - Cheltenham) = -357= -0.00174//. 



It was pointed out by L. A. Bauer- in 1907 that if this relation be correct, the Potsdam 

 standard in 1904 gave values of H too low on the order of .001//, whereas it had been shown- 

 that the Cheltenham standard gave values about 0.001// too high. This conclusion has 

 been verified; for, since the publication of Linke's result, the Potsdam Observatory has 

 found that for the period March 24, 1904 to April 30, 1905, its values of the horizontal 

 intensity, because of a torsion error, required to be increased' by 12.57= +0.00066//. 

 Hence from the Potsdam corrected //-values: 



id) Potsdam-Cheltenham =-0.00108// (1904, corrected). 



From the C. I. W. comparisons at Cheltenham, 1908-10, it was found (Table 7B, 

 series I, II, and III, p. 228) that: 



(e) C. I. W.- Cheltenham = -0.00088// (1908-10). 



If we may assume that the relation between the Potsdam corrected standard and the 

 Cheltenham standard, for which it is known that the same constants have been used through- 

 out, has remained unchanged between 1904 and 1910, we can combine {d) and {e) and get: 



(/) C. I. W.- Potsdam =+0.00020// (1904-10); which is in excellent agreement with 

 the directly-observed quantity (+0.00024//) given above in Table 20 B. 



We might also get an approximate check from the C. I. W. comparisons at the Samoa 

 Observatory, where from 2 sets on May 3, 1906, it was found (p. 257) that C. I. W. Samoa 

 (Tesdorpf No. 1975 referred to Potsdam) = +0.00046//. From the data at hand, it can not 

 be determined definitely, however, just how far, in the .standardizations of Tesdorpf No. 

 1975 at Potsdam, all corrections for the Potsdam standard have been taken into account. 

 An indirect and approximate check can also be derived by means of Dubinsky's preliminary 

 results at Kew and Potsdam in 1908. Referring to Table 31 A, p. 270, it is found that (Kew 

 Potsdam) is 0'.5 (for declination), +0.00011// (for horizontal intensity), and +1'.6 (for 

 inclination). With the aid of the C. I. W. comparisons at Kew in March 1908 and March 

 1910 (Tablesl4A,14B,andl4C, pp. 241-242)wefind that (C. I. W.-Pot.sdam) is +0'.2 (for 

 declination), +0.00018// (for horizontal intensity), and O'.l (for inclination). It will 

 be seen that these indirect results for declination and inclination are in satisfactory agree- 

 ment with the directlj'-observed values given in Tables 20 A and 20 C. Combining the 

 two approximate H checks (+0.00046// and +0.00018//), giving the latter double weight, 

 we get +0.00027/?, against the directly-observed value, +0.00024//, found in Table 20 B. 



'Linke, F. Vergleich der Messung der Horizontalintensitat des Erdmagnetismus in Potsdam und Cheltenham ira 

 Jahre 1904; Nach. Gesell. der Wissenschaften, Gottingen, Math.-Phys. KL, 1907. 



'Bauer, L. A., Preliminary note on an "international magnetic standard"; Terr. Mag., v. 12, 1907, p. 162. 



'Ergebnisse der magnetischen Beobaehtungen in Potsdam, in den Jahren 1903 und 1904, Berlin, 1908, p. xvi, and 

 Ergebnisse . . . im Jahre 1905, Berlin, 1908, p. 16. 



