09 1 



iiiide)' investigation is placed, so that as regards this a rougli adjust- 

 ment will be sufficient ; the exact opposite holds when it is desired 

 to place a body at the place of maximum action. 



There are cases, however, in which only the method of maximum 

 attraction can be applied, e.g. when the susceptibility depends on 

 the field or when the available quantity of the substance is limited 

 (e.g. on account of its rarity). 



On the ground of the above considerations we have made it our 

 object to construct a piece of apparatus lohich in the first place is 

 suitable for measurements loith objects in the shape of an elonqated 

 cylinder, which may further, without important change, be adapted' 

 to the study of small objects placed at the point of maximum-attraction 

 and finally, in addition to being suitable for solids, may also be 

 used for the investigation of liquids, either by enclosing them in the 

 movable part of the apparatus or by surrounding it as a bath. 



The ease with which our apparatus may be adapted to the various 

 requirements has shown itself a great advantage in our experiments ^). 



§ 2. General arrangement of the apparatus (comp. figure and 

 perspective drawing). The main part of the apparatus is a carrier 

 movably suspended along the axis of an enclosure which has the 

 shape of a body of revolution. This enclosure is closed airtiglit, 

 seeing that it must be capable of being exhausted and that it must 

 be possible to maintain throughout the apparatus any pressure below 

 atmospheric. This requirement from the side of ciyogenics has its 

 influence on the choice of most other parts. 



The carrier the motion of which is guided along the vertical, carries 

 at its lower end the experimental object which is placed between 

 the poles of an electro-magnet with horizontal axis. The magnetic 

 attraction or repulsion acts along the vertical and is measured by 

 compensating it by means of the electromagnetic attraction of two 

 co-axial magnetic coils, one of which is attached to the carrier while 

 the other one is fixed. The force between the two coils is given by 



1) We may here recapilulale the various apparatus which in the mean time 



form the complete scheme planned by us : 



depending on the use of i a. apparatus with ellipsoid (Comm. N*^. 116) 



couples ' b. ,, for crystals (to be constructed) 



„ / c. hydrostatic apparatus (Comm. N". 116) 

 dependme on tlie use oi \ , "^ . /. . • i • lu i, c 



^ ^ I d. apparatus for objects in the shape or 



( spheres or cylinders (this Comm.) 



a. has been used for liquid and solid oxygen, c. for liquid gases, d. for liquified 



or solidified gases and various solids. 



