400 SCIENTIFIC RECORD FOR 1882. 



nickel-plated brass, carefully polished Tvitliin, is closed at one end with 

 ground glass, and at the other with a lens of long focus, through which 

 one looks along the tube towards a source of light. Through two 

 parallel tubulures the air to be examined is drawn into the tube, which 

 is cooled by means of sulphide of carbon traversed by an air current 

 in a metallic envelope round the tube. The changes of aspect in the 

 tube at the temperature of saturation enable one to estimate the dew- 

 point to one-tenth of a degree. {Xature, xxvi, p. 1G8.) 



J. F. D. Donnelly calls attention to the recent perfections introduced 

 into the spectroscope by Mr. Hilger, who has managed to secure in- 

 creased dispersion and an excellent vision of the so-called rain band; 

 the spectroscope is also fitted with a telescope and with a second object 

 glass in front of the slit, for the purpose of bringing light from external 

 objects to a focus on it. (Nature, xxvi, p. 501.) 



The Comity International, representing several countries of Europe, 

 the United States, and South America, has published an important 

 volume of memoirs by Drs. Broch, Pernet, Ren6-Benoit, and Marek, on 

 subjects relating to the determination of units of measure and weight. 



As the intensity of weight varies with the geographical height and 

 position above sea-level, the committee give in their first memoir tables 

 of the ratio of acceleration of weight at the level of the sea for difterent 

 latitudes to its acceleration at latitude 45° (Paris), to which latitude 

 they recommend that all weighings be referred. 



In the second memoir, which relates to the tension of aqueous vapor, 

 certain corrections of hitherto accepted results are also indicated, par- 

 ticularly the errors of calculation in Eegnault's tables, as shown by 

 Moritz, and new tables are given for tensions at all temperatures on the 

 new scale of normal degrees from — 30° to + 101° C. 



With reference to the fixed i^oints of mercurial thermometers, the 

 Comit6 adopted the proposition that the point 0° of the centigrade 

 thermometer should be fixed at the pressure of 760™™, when determined 

 in 45° latitude and at the mean level of the sea. Also at the Congress 

 of Meteorologists at Eome, in 1879, there was adopted the proposition 

 of Dr. Pernet to fix the boiling point of water, 100° C, under the above 

 pressure, so as to render strictly comparable the temperatures observed 

 at different places. Degrees of temperature between these points are 

 called normal degrees. 



Tables are also given by which may be calculated the weight of a 

 liter of pure air in different latitudes and at difterent altitudes. In 

 London (latitude = 51° 30', altitude = G.7'".) the weight is 1.2938 grams. 

 {Nature, August, 1881, xxiv, p. 384.) 



Schloesing, as the result of experiments on the absorption of volatile 

 bodies with the aid of heat, is led to propose the application of his 

 method to the determination of the quantity of nitric acid in the atmos- 

 phere. {Nature, xxvi, p. 24.) 



Mr. C. V. Boys read before the Physical Society, London, a paper on the 



