103 Prof. Magnus's Hydraulic Researches. 



Such disturbing influences are unavoidable, and hence the liquid 

 after some time commences a rotation, which, beginning in the 

 lowest strata, is soon communicated to the whole mass. In 

 consequence of this rotation, a funnel-shaped cavity is formed, 

 which at first is only seen on the surface, but soon draws itself 

 downwards to the aperture. 



38. In order to prevent this funnel-shaped cavity, and indeed 

 all rotation, I used a contrivance consisting of four very thin tin 

 plates, each 0'"-25 high,and O"^- 13 broad, which, as is seen in fig. 13, 

 are joined at right angles to each other in the form of a windlass. 

 It must be so placed on the bottom of the vessel, that the efflux 

 orifice may be exactly in the middle of the space which remains 

 free between the vertical plates. By this means, rotation, except 

 in the immediate neighboui'hood of the efllux orifice, is prevented 

 without hindrance to the regular aftlux of the water. In what 

 follows, I shall call this contrivance the tranquilizer. 



39. The water issued under changeable pressure. This kind 

 of efflux was preferred to that under constant pressure, because 

 it is not possible to keep the level of a liquid constant without 

 disturbing the regularity of its motion. In order that the water 

 might not issue too rapidly, and the changes of pressure take 

 place too quickly, the vessel was made of such dimensions, that, 

 when full, it took more than a quarter of an hour to empty it 

 even when the largest efflux orifices were used, and more than 

 half an hour when the smaller oi'ifices were employed. 



40. This vessel was made of strong zinc plate, 0'"-4 high and 

 O^^'S in diameter. In order that the bottom might remain 

 straight, it was strengthened underneath by a plane wooden 

 board 0°i-02 thick. 



In order to be able conveniently to attach the various efflux 

 orifices, a brass plate 0""21 in diameter and 5 millims. thick, 

 was so placed in the bottom of the vessel that its inner surface 

 was a Httle lower than the rest of the bottom. This brass plate 

 had in its middle an aperture O'^'OS in diameter. Its inner 

 surface was ground perfectly plane, and upon it was fastened, 

 water-tight, a tin plate 1 millim. thick, also quite plane, in the 

 middle of which was the efflux orifice. The tin plate had the 

 same diameter as the brass plate, so that its orifice was right in 

 the middle of that of the brass plate. When the two were fixed, 

 the superior surface was level with the zinc forming the rest of 

 the bottom. It was thereby possible to keep the bottom of the 

 vessel quite plane, and to prevent any hindrance to the motion 

 of water, especially in the neighbourhood of the efflux orifice. 

 As a mixture of wax and oil was sufficient to fasten the tin plate 

 on the polished brass one, it was easy to attach plates with ori- 

 fices of various dimensions. At the under sui-face of the brass 



