146 MR. W. N. SHAW ON HTGROMETRIC METHODS. 



connected with each limb of the manometer. By this means the temperature correc- 

 tion is very ingeniously compensated, and, moreover, a second determination can be 

 made with the same apparatus by using the other bottle. 



MATERN* also uses the compensation by a second vessel, but the vessels are glass 

 cylinders, provided with lids ground flat, so that they can simply be laid on. The 

 necessary connexions, &c., are sealed into the lids. The method he suggests is 

 that of finding the increase of pressure, due to the saturation of the air, by allowing 

 water to drop into one of the vessels on to blotting paper. He also givest a simplified 

 form of the instrument for more rapid use. 



I have not been able to find any series of observations showing the comparative 

 results obtained with these different instruments : they have been tried by their 

 inventors, but means of comparison are not at hand, except for SCHWACKHOFER'S 

 instrument, as already mentioned. 



NOTE B. 

 HYGROMETRICAL TABLES. 



It may be useful to add a statement with reference to the tables at present in use 

 by meteorological observers in different countries for the reduction of wet-and-dry-bulb 

 observations. Mr. R. H. SCOTT has very kindly supplied me with the following list 

 of original hygrometrical tables : 



HAEGHENS ('Annuaire de la Socie'te' Me'te'orologique,' 1849), followed by RENOU, 

 France, and DENZA, Italy. 



WILD (' Repertorium filr Meteorologie,' vol. 1, St. Petersburg, 1870), followed by 

 JELINEK, Vienna, 1876. 



BLANFORD. ' Tables for the Reduction of Meteorological Observations in India.' 

 Calcutta, 1876. 



GLAISHER. 'Hygrometrical Tables,' 7th edition. London, 1885. 



GUYOT. " Psychrometrical Tables," ' Smithsonian Miscellaneous Collections.' 

 Washington, 1887. 



Of these HAEGHENS'S and WILD'S tables are millimetre-centigrade tables founded upon 

 REGNAULT'S table of pressures and the psychronaetric formulae of the same authority, 



viz. : 



_ 0-480 (*-Q 

 610 - if ' 



0-480 (t - Q 

 689 - t' ' 



* ' WIEDEMANN, Annalen,' vol. 9, p. 147. 

 t ' WIEDEMANN, Annalen,' vol. 10, p. 149. 



