Intelligence and Miscellaneous Articles. 419 



3. ' Boring on the Booysen Estate, Witwatersrand/ By D. 

 Telford Edwards, Esq. 



An account is given of a boring on the Booysen estate, situated 

 about 2 miles from Johannesburg, and about 5000 feet south of the 

 nearest point of outcrop of the ' Main Reef ' of the Witwatersrand. 

 The ' Bird-Reefs ' crop out generally at a distance of 4000 feet 

 south of the Main Reef. 



The borehole, 1020 feet deep, passed through sandstones (often 

 micaceous), quartzites, and conglomerates, the last-named having a 

 collective thickness of 91 feet 7 inches, the two thickest reefs 

 being respectively 26 and 22 feet thick. The dip of the beds 

 was 35°. Traces of gold were obtained. All the reefs were 

 highly mineralized, principally with iron-pyrites, and belonged to 

 the ' Bird-Reef ' series which overlies the Main Reef. 



XL. Intelligence and Miscellaneous Articles. 



MOLECULAR ENERGY OF GASES. 

 To the Editors of the Philosophical Magazine. 



GENTLEMEN, 



IT is a pity that Dr. Gore did not notice that the entries in the 

 column on page 340, which he calls "square of molecular 

 velocity," are nothing but a certain number (probably intended for 

 3395175) divided by the molecular weight of successive substances, 

 and that when he multiplies the numbers in this column by the 

 respective molecular weights again, the only ground for surprise is 

 that the results do not come out identical. The numbers in his 

 last column would in fact be all precisely the same were it not for 

 a few arithmetical errors in the working. 



Agreement to 4 figures (or to 7 for that matter) should always 

 be suspected, especially since molecular weights themselves are 

 not known accurately to 3 places. If Dr. Gore is still inclined to 

 attribute importance to his figures, he may convince himself by 

 inventing hypothetical substances with comic molecular weights 

 and finding that they obey his law equally well. 



As I understand him, however, he writes to request information 

 as to what is known about molecular kinetic energy. A good deal 

 is known ; for instance the following : — 



The mean square of molecular velocity is given for perfect 

 gases by 



and since p varies as the molecular weight, for different gases at 

 the same temperature, it follows that the average kinetic energies 

 of the molecules of all permanent gases at the same temperature 

 and pressure are the same. 



But this statement does not hold for imperfect gases or vapours, 

 because for them the external or applied pressure is not expressible 

 so simply in terms of velocity, but is something more like 



