198 Proceedings of the Boyal Society of Edinburgh. 



of the sky is developed precisely in proportion to the probable 

 existence of vapour in that critical stage of condensation which 

 should render it colorific. And he applies the same reasoning to 

 account for the prognostics of weather, drawn from the redness of 

 the evening and morning sky. 



Fehriiary 18. — Dr Abercrombie, Vice-President, in tlio 

 Chair. The following communications were read : — 



1. Notice of some observations made during the Storm of Ja- 



nuary 1839. By John Scott Russell, Esq. 



2. On Fresnel's Law for the Intensity of Reflected and Re- 



fracted Light. By Professor Kelland. 



March 4. — Dr Hope, Vice-President, in the Chair. The 

 following communications were read : — 



1. On a new Galvanic Battery, and an improved Voltameter. 



By Martyn Roberts, Esq. Communicated by Sir John 

 Robison. 



2. Notice upon the Alcoholic Strength of Wines. By Dr 



Christison. 



Various accounts have been given of the alcoholic strength of 

 wines by Mr Brande, Julia-Fontenelle, and others. The author 

 has been engaged for some time in experiments for determining 

 the proportion of alcohol contained in various wines of commerce, 

 and also the circumstances which occasion a variety in this respect. 

 The present paper is an interim notice of the results. 



The method of analysis consisted in the mode by distillation, 

 which was applied with such contrivances for accuracy that nearly 

 the whole spirit and water were distilled over without a trace of 

 empyreuma, and without the loss of more than between 2 and 6 

 grains in 2000. From the quantity and density of the spirit, the 

 weight of absolute alcohol of the density 793.9, as well as tlie volume 

 of proof spirit of the density 920, was calculated from the tables of 

 Richter founded on those of Gilpin. 



The author has been led to the general conclusion that the al- 

 coholic strength of many wines has been overrated by some expe- 

 rimentalists, and gives the following table as the result of the in- 

 vestigations he has hitherto conducted. The first column gives the 

 per-centage of absolute alcohol by weight in the wine, the second 

 the per-centage of proof spirit by volume. 



Port — Weakest, . . ... 



Mean of 7 wines. 

 Strongest, . . ... 



