1864.] 



Prof. Guthrie on Drops, 



473 



glycerine forms the medium through which mercury drops. In this case, 

 when gt=b", there are always two supplementary drops of mercury formed. 

 It is impossible to determine whether they both have their origin at the 

 same moment and from the same drop. The probability, however, is that 

 they have not, but that one is first separated from the main drop, and the 

 second from the first ; for there is always a great disparity between the 

 sizes of the two supplementary drops, whereas, if they were both formed 

 at the same time and for the same reason, we should be justified in expect- 

 ing greater equality. The drops soon separate in falling, in consequence 

 of the difference of their surfaces. The relative sizes of the main and sup- 

 plementary drops in the case of mercury falling from copper through gly- 

 cerine were determined as follows : — A number of porcelain cups (fig. 9) 

 were arranged at the bottom of a shallow dish full of glycerine ; when the 

 rate of dropping was uniform at fft=4"j the dish was shifted horizontally 

 so that every drop with its two supplements was caught in a separate cup. 

 The globules of mercury in each cup were removed by a little scoop of 

 copper foil. Ten of each kind were collected. After washing and drying, 

 they were weighed, with the following result : — 



Table XlY~Mercurtj. 



fft=4". 

 T=21°-3 C. 

 Radius of sphere = 12-8 millims. 



grms. 



10 principal drops weighed 6*3447 



10 first supplementary drops weighed .... 0'1242 

 10 second do. do. do 0-0229 



10 complete drops weighed 6*4918 



In all cases of SLL the supplementary drop or drops were collected and 

 weighed or measured with the main drop. 

 In Table XV.— 



Column 1 shows the medium through which the mercury dropped. 

 Column 2. The number of drops weighed. 



Column 3, The weight of the drops. The weight of every batch of drops 

 is given, in order that the approximation between the figures for each liquid 

 may be compared with that between the separate liquids. In two cases 

 only, marked by an asterisk, are the numbers probably erroneous. They 

 are not reckoned in taking the mean. 



Column 4. Mean weight of single drop, from column 3. 



Column 5. Specific gravity of medium. 



Column 6 shows the weight of the drop of mercury in the liquid. Since 

 the falling of the drop is determined in part by its weight, and since the 

 weight depends not only upon the size of the drop, but also upon the den- 

 sity of the medium in which it is formed, it is interesting to see how the 



VOL. XIII, S N 



