276 Mr. C. Tomlinson on the Action of Solid Bodies 



a quantity which represents the energy of restoration of the ho- 

 mogeneous condition. Again, since the mixture is not homo- 

 geneous in respect of its temperature, the restorative function 

 will be affected by the velocity of convection. It is easy to show 

 that formula (II.) is true for a non-homogeneous mixture if 

 such mixture is a perfect liquid. This view shows that (II.) 

 applies to liquids approaching the perfect condition, but does not 

 apply to syrupy liquids, to thick oils, and such like. The dif- 

 ferential formulae for these show a tendency to thickening at the 

 top, and also at the point of application of the heat. This ten- 

 dency increases with the viscosity, and after a certain point may 

 become cumulative, the energy of convection and heat-conduct- 

 ing power of the mixture as it approaches the solid state deter- 

 mining where the cumulative effect will first begin. Attention 

 must also be paid to the direction of the heat-convection, i. e. 

 the direction in which the warmer currents'now. Thus, if the 

 convection of water at a temperature above that of its point of 

 maximum density be reckoned positive, its convection below the 

 temperature of the said point must be taken as negative. The 

 deduction of the differential form of (II.) for a non-perfect liquid 

 is not the object of this paper, which was commenced merely to 

 give a simple means of correctly calculating r from Mr.Wanklyn's 

 theory ; but I may state that the correct formula? show that a 

 crust may be formed in two ways — (1) by negative convection, 

 (2) by increase of viscosity accompanied by very slight variation 

 of temperature in the parts of the evaporating liquid, or by very 

 slow evaporation, or by a very great difference of temperature 

 between the liquid and the " space " immediately beyond it. 

 February 22, 1873. 



Note.— On examining the theory by which I was led to for- 

 mula (II.), I find that if the energy of return to homogeneity 

 remains sensibly uniform for all mixtures from a-\- h to ar + b, the 

 proposed formula holds, provided the mixture does not pass du- 

 ring the operation through a point of maximum or minimum 

 density. 



February 24, 1873. 



XXXVI. On the Action of Solid Bodies on Gaseous Super- 

 saturated Solutions. By Charles Tomlinson, F.R.S.* 



IN the March Number of the Philosophical Magazine I gave 

 a translation of Dr. Henricr's paper on the above subject 

 from PoggendorfPs Annalen for December last. Having also 



* Communicated bv the Author. 



