ON COMPARING AND BEDUCINa MAGNETIC OBt>EUVATIONS, 33S 



Appendix V. Communication from Sir H. Lefroy to the Secretary 



August 6, 1887. 



The millimetre curve paper recently engraved by the Kew Committee, 

 in accordance with the resolution of the International Polar Conference, 

 will be of infinite service in enabhng ready comparison to be made of 

 mean results at different stations of observation. I have employed it in 

 bringing together the mean solar-diurnal curves of dechnation, including 

 all disturbances, for the winter months at stations on the American 

 continent, namely — 



Floeburg Beach . 

 Discovery Harbour 

 Fort Conger (Greely) . 

 Van Rensellaer Harbour 

 Point Barrow 



Fort Confidence, Bear Lake 

 Fort Rae, Slave Lake . 

 Lake Athabasca . 



To which I have added — 



Polhem, 8i3itzbergen 



Island of Jan Mayen . 



Kingua Fjord, Cumberland Sound 



By M.P. is meant Ross's Magnetic Pole in lat. 70° 5', long. 96° 43'. 



It results that the first five curves on the list bear a strong re- 

 semblance to each other, especially in the exceptionally strong develop- 

 ment of the mid-day curve, due to a preponderance of westerly disturb- 

 ances when the sun is near the meridian ; the next three, and the 

 observations of the Swedish Arctic expedition to Spitzbergen in 1872-73, 

 show an equally marked development of the night curve, due to a 

 preponderance of easterly disturbances, having their maximum effect 

 from 5 to 7 a.m. Captain Creak has remarked that at Discovery Bay 

 ' the disturbing force during the day, that is, from 8 A.M. to 8 P.M., is 

 considerably greater than that during the night between 8 p.m. and 

 8 A.M.' This is the reverse of what has been found in lower American 

 latitudes ; and it is especially remarkable that, if we complete the curve 

 for Fort Confidence on Great Bear Lake by hand, for the hours of 

 the night when observations were not taken, it is the case at that 

 relatively southern station also, although the feature is conspicuously 

 absent at Fort Rae on Great Slave Lake. It appears, therefore, that 

 there is a region round the magnetic pole where westerly disturbances 

 prevail, outside of which easterly disturbances prevail. This region 

 extends towards the S.W. about 500 miles, but towards the N.E. as 

 much as 850 miles. The Spitzbergen curve, notwithstanding the high 

 northern latitude of the station, has the characteristics of more southerly 

 stations on the American continent, as has also that of the Island of 

 Jan Mayen. The curves at Great Slave Lake and Point Barrow closely 

 resemble each other. Kingua Fjord on Cumberland Sound has the 

 northern characteristics. I have dealt with the winter months only, 

 because many of the stations were only occupied in the winter, and with 

 the natural mean curves as affected by disturbance, for simphcity, because 

 there is ample evidence that their exceptional character as compared 

 with places distant from the magnetic pole is wholly due to what we 

 call disturbance ; and the few stations where the total disturbance has 



