292 Mr. Konig on the Formation of Capillary Copper. [Oct. 



adds to the probability, that not only a great portion of capillary 

 native copper, but also silver (especially that from Peru, in the 

 hollows of porous iron-shot quartz) is produced by the same 

 agency, and under similar circumstances. It may not, there- 

 fore, be uninteresting to Mr. Smithson to learn, that the above 

 remarkable fact, communicated by him in the Annals of Philoso- 

 phy for April, on the authority of M. Ampere, is already men- 

 tioned by Sir James Hall, in his account of the experiments on 

 the effect of heat modified by compression. A substance like 

 •wool was formed in several of those experiments by the exuda- 

 tion of the fusible metal tbrough the barrels of iron employed by 

 him ; the metal in a liquid state spouting to a considerable dis- 

 tance. There is some of this metallic wool among the speci- 

 mens, showing the result of his experiments, and deposited by 

 Sir James Hall in the British Museum. 



Believe me, dear Sir, very truly yours, 



Charles Konig. 



Article VII. 



On Wollaston's Thermometer, and its Application in Measuring 

 Heights. By James Apjohn, AB. MD. 



(To the Editor of the Annals of Philosophy.) 



SIR, Trinity College, Dublin, Aug. 18, 1821. 



Though the Rev. Dr. Wollaston, to whom the credit of the 

 invention of the thermometrical barometer is undoubtedly due, 

 has transmitted to the Royal Society two papers describing its 

 construction, and some measurements made with it, still he does 

 not appear to me to have sufficiently explained its principle, or 

 to have duly appreciated its importance. A few remarks on 

 these topics may, therefore, prove not unacceptable to those who 

 have not hitherto directed their attention to this subject. It is 

 a curious and well-known fact, that the boiling points of liquids 

 are lowered under diminished pressure ; and it has frequently 

 occurred to philosophers, that this discovery might be turned to 

 account for the purposes of levelling. All that would appear 

 necessary for putting this method into practice would be the 

 possession of a very delicate thermometer, and a knowledge of 

 the law which indicates the relation between a given fall or rise 

 in the boiling point of water (for example), and the corresponding 

 ascent or descent. Now if from the observation of the boiling 

 points at any two stations, we can infer the pressures due to 

 those temperatures, it is clear that the problem is solved, and 

 that the subsequent calculation is to be conducted as if the den- 



