350 Messrs. Thomson and Wood on tlte Composition of 



of heat, whether we suppose the pressure equal in all direc- 

 tions, or adopt any otlier hypothesis. Accordingly, when we 

 adopt the equations which are obtained on the usual theory, 

 and suppose the initial condensation and initial velocity given 

 arbitrarily as functions of r, no contradiction is arrived at, 

 either in the general case (see Phil. Mag., vol. xxxiv. p. 5.5, 

 paragraph marked 2), or in the particular case which might 

 seem beforehand most favourable to tlie contradiction (see 

 paragraph 3), as might have been confidently anticipated, 

 inasmuch as one truth cannot contradict another. 

 Pembroke College, April 12, 1849. 



LI. Note on the Composition of Shea Butter and Chinese 

 Vegetable Tallow. By Dr. R. D. Thomson a7id Mr. 

 Edward T. Wood*. 



^HEA Butter. — This substance is a vegetable product of 

 Western Africa, and was brought into notice by the cele- 

 brated Mungo Park during his journey in 1796. The tree 

 from which it is procured he describes as very much resem- 

 bling the American oak, and the fruit (from the kernel of 

 which, being first dried in the sun, the butter is prepared by 

 boiling the kernel in water) has somewhat the appearance of 

 a Spanish olive. The kernel is enveloped in a sweet pulp 

 under a thin green rind, and the butter produced from it, 

 besides the advantage of keeping the whole year without salt, 

 is whiter, firmer, and, according to Park, of a richer flavour 

 than the best butter he ever tasted made from cows' milk. 

 The growth and preparation of this commodity seem to be 

 among the first objects of African industry, and it constitutes a 

 main article of their inland commerce. This butter is abun- 

 dantly produced, not only towards the Gambia, but also in 

 the countries adjoining the Niger, as it is mentioned by the 

 Landers and other recent travellers. Mr. John Duncan, who 

 penetrated by Dahomey, describes the tree as resembling a 

 laurel, and growing to the height of eighteen or twenty feet. 

 The leaf is somewhat longer than the laurel and a little broader 

 at the point. The nut is of the size and form of a pigeon's 

 egg, and of a light brown colour; the substance of the shell 

 about that of an egg. The kernel when new is nearly all 

 butter. The shell is crushed from the kernel, which is also 

 crushed and boiled with a little water in a pot for half an hour ; 

 it is then strained through a mat, when it is placed in a grass 



• Read before the Philosophical Society of Glasgow, April 26, 1848. 



