INVESTIGATED BY THE METHOD OF JET VIBRATION. 361 



The greatest error is, expressed in per cent., 



A = 

 For 



b/n = 0-1 0-2 0-3 0-4 



A = 0-04 0-16 0-35 0'65. 



For the values of bja here used this error is without importance. 

 For the "jet-catcher" used here 



L, = 2-97985 cm., L, = 2'99225 cm,, L = Li + L, = 5'9721 cm. 



The whole of the "jet-catcher," with the exception of the before-mentioned steel 

 plates, is made of magnalium, which is both light and keeps in good condition. Before 

 use the "jet-catcher" is dipped in melted paraffin, so that it is covered with a thin 

 layer, removed only from the edges of the knives, Ic. 



In order to prevent evaporation during weighing it is necessary to cover the 

 openings of the "jet-catcher"; this is done by the help of two indiarubber plates 

 fastened to two metal rods, pressed against the two openings by help of springs. It 

 is also necessary to introduce a correction for evaporation during the cutting off, as 

 described below. 



The measuring itself takes place in the following manner : The fluid contained in 

 the "jet-catcher" from a previous measurement is completely removed and the apparatus 

 is carefully cleaned. The indiarubber coverings are set and the "jet-catcher" is 

 weighed and arranged on the pendulum, whereupon the rubber covers are removed 

 and the pendulum carried up to a horizontal position, released and allowed to 

 complete five whole swings, after which it is caught again. As soon as this takes 

 place the rubber covers are put on, the "jet-catcher" is taken from the pendulum and 

 all outside drops removed, after which the weighing takes place. After the conclusion 

 of the remaining measurements, which takes place in the course of a few minutes, the 

 jet is stopped and the " jet-catcher " again arranged on the pendulum. The rubber 

 covers are removed and the pendulum is allowed again to complete five whole swings, 

 beginning with the same height as with the " cutting off," after which the rubber 

 plates are replaced and the "jet-catcher" weighed again. If we call the weight of the 

 liquid contained in the "jet-catcher" by the first weighing P mg., and by the second 

 P p mg., then the loss by evaporation during these swingings is p mg. The whole 

 weight of the quantity of the liquid cut off the jet is then P + a. p mg., as the loss by 

 evaporation during the cutting off is op mg. 



The determination of the coefficient a takes place as follows : Two cuts are made, 

 the pendulum completing only one whole swing. The quantity of liquid " cut off" is 

 determined in the ordinary manner, after which the loss of weight, p lt for five whole 

 swings of the pendulum is determined as explained above. Next four cuts are made, 



VOL. ccvn. A. 3 A 



