﻿324 Intelligence and Miscellaneous Articles, 



right angles to the first, and again being broken up. If it forms 2 . 3, 

 2 . 4, and so forth nodes, it will be seen that on each elongation it 

 forms a star with 3 or 4 rays and 3, 4, &c. indentations ; if, then, 

 the time between two elongations is small enough, a star of 2 . 3, 2 . 4, 

 &c. rays will be formed. 



The force which opposes the disruption of the drop is, beside 

 molecular attraction, the pressure of the vapour which escapes at the 

 side of the drop. Vapour will keep the drop so much the more 

 together the more it is compelled by the form of the dish to press 

 against its sides, therefore the more the dish is curved. The for- 

 mation of nodes will be the more abundant the greater the resistance 

 offered to expansion, and therefore the greater the curvature. It 

 will thus be seen that the shape of the drop mainly depends upon 

 the shape of the dish ; and the following connexion is observed. 



1. Very flat, almost plane dishes furnish with about 1 cub. centim. 

 water (f cub. centim. alcohol, \ ether) almost always the shape of 

 crossed ellipses. If the curvature is very uniform, the shape remains 

 constant as the drop diminishes. With large drops of water the 

 motion is so slow that all the individual phases can be easily followed, 

 especially the first rise of oscillations from a bubble of steam seek- 

 ing to burst through. Alcohol and ether move more quickly. 



2. More highly curved dishes give shapes with more than four 

 nodes, the number of nodes increasing with the decrease of the radius 

 of curvature, until at about 1|-", owing to the diminution of the con- 

 tents of the dish, there is again a decrease. 



With the gradual diminution of the drop, which is caused by its 

 evaporation, the circumference ultimately becomes too small for the 

 original number of nodes ; a pause then occurs, followed by new 

 vibrations with fewer nodes. The above statements refer primarily 

 to the largest forms, and in my experiments have been found to 

 hold for these with such certainty that, by choosing the dishes, I 

 could produce definite stars (to as many as 16-rayed ones) with 

 a probability of more than T ^-. Dishes not too smooth (copper for 

 instance) are advantageous, since small roughnesses promote the vi- 

 brations. Very steady drops are obtained with small quantities of 

 water (diameter of the spheroid 0'8 to 1 centim.) in a very smooth 

 silver dish heated as gently as possible. 



The formation of the smaller waves which almost always ruffle the 

 surface of the drop, I should ascribe to the vapour, which in esca- 

 ping brushes over the sides and bottom of a drop as a violin-bow 

 across a string. These vibrations may also become audible ; their 

 tone is a deep, gentle humming, but definite ; to hear it, all noise 

 from the flame must be avoided, even the heating-flame, of course 

 only after the dish has been so far heated that its temperature is 

 maintained for a time ; a confusion of the note with the crackling 

 which takes place just before the drop bursts is not very possible. — 

 PoggendorfTs Annalen, No. 1, 1871. 





