REPORT OF THE SECRETARY. 31 



verification or disproval of the many empirical rules which have been 

 proposed and are used for predicting the weather,. &c. The exten- 

 sive series of observations made by Dr. S. P. Hildreth, of Marietta, 

 Ohio, mentioned in a previous report, belong to the same class, and 

 will also be inserted in the volume above mentioned. 

 ■ We have already referred to the additions to the meteorological 

 tables of Professor Gnyot, and stated that it is proposed to still fur- 

 ther increase these tables by a series intended to facilitate the calcu- 

 lation of the mean direction of the wind. 



The directions and blanks for making meteorological observations 

 which have been prepared and published at the expense of the In- 

 stitution have been extensively distributed in this country, and trans- 

 lated and reprinted abroad. The geographical and statistical society 

 of Mexico has recently adopted them, and signified the intention of 

 cooperating with the Institution in extending its system of observa- 

 tions more widely over this continent. Were not our general system 

 of meteorology interrupted by the discontinuance of the reception of 

 observations from the southern States, this would be an important 

 addition to. our means of tracing the extent of disturbance of the 

 atmosphere which accompanies our winter storms. 



Professor Guyot availed himself of a visit which he made to Europe 

 last year to establish by his own observation the relation of the 

 standard barometers used by the Institution to the most important 

 standards of the European observatories. The comparisons were 

 made by means of two Forfm barometers, with cistern of constant 

 level, as modified by Ernst, of Paris, and constructed several years 

 ago by that skilful artist for the Institution. Both instruments had 

 been previously tested by long usage, and just before leaving this 

 country their relation to a large standard barometer by Newman, of 

 London, and a large sized barometer by Ernst, was ascertained by a 

 series of numerous comparisons made with great care. These two 

 instruments were directly compared in Europe with a standard 

 barometer at Kew observatory, now acknowledged as the nor- 

 mal barometer among English meteorologists, and with the stan- 

 dard instruments at the Brussels, Berlin, and Geneva observatories, 

 by the kind permission and assistance of the directors of these several 

 institutions, Professors Stanley, Quetelet, Enke, and Plantamour. 

 The last set of comparisons at Geneva, Switzerland, was found par- 

 ticularly useful from the fact that by the untiring care of Professor 

 Plantamour the relation of his barometer has been fully established 



