New Method of Photometry 1 59 



that his own experiments made him doubtful whether a 

 sufficient quantity of soot could have been distributed 

 through the atmosphere to produce the blackness described. 



Colonel Sykes then gave an account of a balloon ascent, 

 made under the auspices of the Meteorological Committee 

 of the British Association. But as the balloon unfortunately 

 was not of the stipulated capacity and very leaky, it had 

 only risen to the height of a mile and a half, and its final 

 descent had been rather dangerously rapid. Professor 

 Tyndall suggested the erection, at an elevation of 14,000 feet, 

 of a permanent hut for scientific observations, 1 such as 

 determining whether the solar spectrum is of the same length 

 as at lower positions, whether as many obscure rays are 

 present in it, and whether its red end is longer. 



May 22nd, isgth meeting. Professor Dove, 2 of Berlin, 

 described a new method of photometry. When micro- 

 photographs of inscriptions are viewed through a microscope, 

 they appear, with transmitted light, black on a white ground, 

 but with reflected light, white on a black ground. By using 

 both kinds of light, and due graduation, the one can be 

 made indistinguishable from the other, and if the lights to 

 be compared are adjusted, so that the one is transmitted 

 and the other reflected, their relative intensity can be 

 estimated from the amount of movement required by the 

 microscope. In a similar way the illuminating power of 

 different coloured lights can be compared. 



Professor Wurtz, 3 of Paris, gave an account of the method 

 of reconverting aldehyde into alcohol by digesting it with 

 an amalgam of sodium. 



x That has now been done. Besides the Gniffetti Hut, at 11,877 feet, 

 there are now the Regina Margherita Hut at 14,961 feet, both on the 

 Italian side of Monte Rosa (see Angelo Mosso, Life oj Man on the High Alps 

 (Translation 1898)), and the Vallot Observatory at 14,320 feet on Mont 

 Blanc, besides that erected on the summit by M. Janssen (now removed). 



2 Heinrich Wilhelm Dove (1803-1876), Professor of Natural Philosophy 

 at Berlin for many years, made important investigations in optics and 

 electricity, and did much to establish meteorology on a scientific basis. 



3 Charles Adolphe Wurtz (1817-1884), born at Strasburg, resident in Paris 

 from 1844, an eminent chemist and author of several works, two of which, 

 The Atomic Theory and Modern Chemistry, have been translated into English. 



