1876.] 



On the Forms assumed by Drops of Liquids. 



261 



XXVIII. On the Forms assumed by Drops of Liquids falling ver- 

 tically on a horizontal Plate/^ By A. M. Worthington. 

 Communicated by 11. B. Clifton, M.A., F.R.S., Professor of 

 Experimental Philosophy in the University of Oxford. Re- 

 ceived May 17; 1876. 



My attention was first drawn to the subject o£ this paper last spring, 

 by Mr. H. P. Newall, o£ the P-ugby School Natural-History Society, who 

 showed me the mark made by drops of water and mercury falling on a 

 smoked glass plate, the lampblack being swept away in concentric circles 

 and radial striae. The patterns thus left were generally symmetrical and 

 beautiful, and varied with the height of fall of the drop. I have 

 since sought to investigate the cause of these appearances in Prof. Helm- 

 holtz's laboratory in Berlin. 



My first care was to obtain a series of what I will call " patterns " left 

 by drops of various liquids, of various and measured diameters, falling 

 from various and measured heights on horizontal smoked glass plates. 



I experimented with water and mercury as types of hquids which do 

 not wet the lampblack, and with alcohol as a type of those which do. 

 Drops of a constant size were obtained with water and alcohol by allow- 

 ing the liquid to fall, drop by drop, from the end of a vertical capillary 

 tube. In the case of mercury, a narrow vertical glass tube was provided 

 at its upper end with a closed caoutchouc tube ; the pressure of the hand 

 on this expelled the air, and a column of mercury, about 60 millims. in 

 length, was drawn up by suction to be expelled when required, drop by 

 drop. The caoutchouc tube was found preferable to a hollow caoutchouc 

 ball, as by wrapping it round the finger the internal volume could be 

 diminished more gradually and regularly than with the ball, and thus the 

 danger of expelling more than the normal-sized drops, whose diameter 

 should depend only on the internal diameter of the tube, was diminished. 

 This danger was, however, only completely avoided in later experiments 

 by using an inclined glass tube, to the lower end of which an open caout- 

 chouc tube was attached, whose upper end could be raised or lowered at 

 pleasure, and the mercury in the U-shaped tube thus formed brought to 

 the level of the mouth of the glass tube, and made to fall over drop by 

 drop. The drops thus obtained were found to be very constant in mag- 

 nitude. The diameters of the drops were calculated from the weight of 

 10, 15, 20, or 30. The height of fall was taken as the distance between 

 the plate and the bottom of the vertical or the lower edge of the inclined 

 tube. The glass plates were smoked in the flame of a stearine candle : in 

 cases where the height of fall was great, the adhesion of the smoke was 

 increased by dipping the plate in petroleum or turpentine, and gently 

 wiping before smoking. I thus obtained a large number of patterns ; 

 and examination of them showed the extreme difficulty of explaining 



