of a Liquid Mass without Weight. 451 



A pivot, 25 millims. high, carrying a magnetized needle 10 

 centims. long, was fixed at the centre of a cylindrical glass dish, 

 11 centims. in internal diameter and 6 centims. deep. In making 

 an experiment, the liquid to be examined was poured into the 

 dish until it just came up to the lower face of the needle ; next, by 

 means of a bar-magnet, the needle was turned through 90° from 

 the magnetic meridian, and kept in that position Until the surface 

 of the liquid bad again become motionless ; then the bar-magnet 

 was suddenly removed and the time observed that the needle 

 took in traversing a given angle : in my experiments this angle 

 was 85°. When this time had been observed, more liquid of 

 the same kind was added until the needle was covered to a depth 

 of about 2 centims., the interior of the cap of the needle was 

 freed from the small quantity of air which it contained, and 

 under these new conditions the time occupied by the needle in 

 traversing the angle of 85° was determined as before. 



Experiments of this kind were made with five liquids of the 

 first category, namely, water, glycerine, and saturated solutions 

 of carbonate of sodium, nitrate of potassium, and chloride of 

 calcium. Now, although it would seem that the needle must 

 experience about twice as little resistance at the surface of the 

 liquid as it does in the interior, nevertheless for each of the 

 above liquids its velocity was much less in the former case than 

 it was in the second. With water, for instance, in one series of 

 observations the mean time occupied in traversing 85° at the 

 surface was 4*59 seconds, while in the interior it was only 2*37 

 seconds. Consequently it is evidently necessary to assume that 

 the surface of these liquids opposes a special resistance to the 

 movement of the needle, or, in other words, that the superficial 

 layer possesses a viscosity proper to itself and much greater 

 than the interior viscosity. We may add that if, while the 

 needle is kept at the surface at an angle of 90° from the mag- 

 netic meridian, any very small light body, such as the smallest 

 fragment of gold leaf, is laid on the surface of the liquid in 

 the meridian, on setting the needle free, this small body is seen 

 to be displaced and to move in the same direction as the needle, 

 whence it follows that the whole surface of the liquid turns to- 

 gether with the needle. 



Five liquids of the second category, namely, alcohol, oil of 

 turpentine, olive-oil, sulphuric ether, and sulphide of carbon, 

 were tried in the same way ; and for each of these the velocity 

 was, on the contrary, greater at the surface than in the interior. 

 With alcohol, for example, the average time occupied by the 

 needle in traversing 85° was 1*48 second at the surface, and 

 3-30 in the interior. Moreover, in the case of these liquids, a 

 small body floating on the surface in the magnetic meridian 



