TERRESTRIAL MAGNETISM. 709 



U depends on the distance between the centres of the two 

 needles, and its value will be determined by using the needle F as 

 a deflector at three different distances. 



Dr. Lloyd thus sums up Ihe advantages of this method (p. 100): — 



*' 1. It is applicable with equal accuracy at all parts of the 

 globe. 



'' 2. It dispenses with the employment of a separate instrument 

 for the determination of the magnetic intensity, and with the 

 separate adjustments required in placing it. 



" 3. The constants to be determined, i.e.^ the magnitude of the 

 added weight, and the radius of the pulley by which it acts, can 

 be ascertained with more ease and certainty than those with which 

 we have to deal in the method of vibrations, and are less liable to 

 subsequent change. 



" 4. The observations themselves are less varied in character 

 than the usual ones, and may be completed in a shorter time." 



13. Magnetic Observations, made during the Austro- 

 HuNGARiAN Expedition, by Lieut. Weyprecht. 



(From Petermann's " Geograph. Mittheilungen," Jan. 1875, 

 and " Nature," March 18, 1875.) 



" In close connexion with the Aurora are the Magnetic disturb- 

 ances ; while these are in our regions the exception, in northern 

 latitudes they are the normal condition ; there the needle scarcely 

 ever remains still at rest. This is the case with Declination as 

 well as Intensity and Inclination needles. As long as the ship 

 drifted, which was till the October of the second year, it was, of 

 course, impossible to put up the fixed Variation instruments. We 

 did, however, often carry out absolute observations with Lament's 

 magnetic theodolite, but it was evident already in Nova Zembla, 

 that, in consequence of continuous disturbances, all these observa- 

 tions, without the contemporary reading of the Variation instru- 

 ments were of very little worth. 



"In November 1873, as soon as it was certain that we were 

 anchored for the winter, I had some snow huts built close together, 

 in one of which the Variation instruments, in the other the 

 magnetic theodolite and the Inclinometer for the absolute observa- 

 tions, as well as the Astronomical instruments were put up. The 

 three Variation instruments for declination, horizontal intensity, 

 and inclination were supplied by Dr. Lament, the Director of the 

 Observatory in Munich, on the pattern of those instruments which 

 are in use there. 



" After the first series of observations, it was evident that the 

 earlier methods of observation, 2.e., simple readings at certain 

 hours, at least in these regions, were worthless, as they depended 

 merely on the accidental amount of the momentary disturbances. 

 They give neither a true mean, neither do they give a picture 

 of the movement of the needles. In former expeditions the 

 recorded observations are much too far apart to render it possible 

 to draw correct conclusions on the magnetic conditions. 



^* Under these circumstances I took quite a difierent course. 

 Every third day, at an interval of four hours, 1 caused minute 



