of Liquids at Common Temperatures. 439 



Capsule. Obs. 1. 2. 3. 4. 5. 6. 7. 8. Sum. 



No. 1 . . . 17 16 8 15 17 16 16 21 = 126 

 No. 2 ... 17 14 16 10 11 17 18 18 = 121 

 No. 3 ... 11 11 19 19 12 10 17 18 = 117 



24)364 

 Mean .... 15| 



The mean duration of a spheroid of common turpentine in this 

 series of observations was 151 seconds. This turpentine was di- 

 stilled off caustic potash, and a similar series of observations 

 immediately made with the fresh distillate. The superior cohe- 

 sive force of the distillate over that of the common turpentine 

 was shown at once by the greatly diminished proportions of the 

 film. The film of the common turpentine was nearly 2-J inches 

 in diameter ; that of the distillate was at first only a flattened 

 drop, which gradually increased in size, by the accretion of other 

 drops, to about the diameter of a florin or half-a-crown. On 

 going through a similar series of observations with these films, 

 the duration of the spheroids was as follows : — 



Capsule. Obs. 1. 2. 3. 4. 5. 6. 7. 8. Sum. 



No. 1 ... 35 33 44 45 33 10 40 40 = 280 

 No. 2 ... 34 41 35 38 35 37 37 33 = 290 

 No. 3 ... 42 43 40 44 34 31 33 33 = 300 



2 4)870 



Mean .... 36± 



So that the mean duration of a globule of the distillate compared 

 with that of the common turpentine is as about 7 to 3. Both 

 the above series of experiments were made on the same morning ; 

 the weather was fine ; the reading of the dry-bulb thermometer 

 gave 62^°, and that of the wet-bulb 55J°. If the spheroidal 

 condition of liquids depends on the existence of a layer of vapour 

 which prevents contact between the globule and the surface 

 beneath, it is quite intelligible why the experiment in this form 

 should succeed better when the evaporative force is strong than 

 when it is weak. Indeed in damp or wet weather the duration 

 of the globules is much diminished ; or it may be difficult to form 

 them at all, even in a warm room. 



That there is no contact between the globule and the film may 

 be proved in several ways : — (1) There is a slight depression in the 

 film just below the globule ; and this depression accompanies the 

 globule when it rolls about, which it sometimes does. (2) The 

 drop may fall with some force from the end of the glass rod, as 

 from the height of an inch, and roll about without being absorbed. 



