6 PREFACE TO THE SECOND EDITION. 



In the Thermometrical series six small tables have been added ; they were 

 prepared for converting into each other differential results given in degrees 

 of any one of the three thermometrical scales, irrespective of their zero 

 point. 



The Hygrometrical series has been entirely reorganized. It only con- 

 tained five tables, all in French measures, and the Appendix. It is now 

 composed of twenty-seven, arranged in three divisions. In the ffrst are 

 found ten tables, based on Regnault's hygrometrical constants, both in 

 French and in English measures, in two corresponding sets, for the use of 

 the psychrometer, the dew-point instruments, and for computing the weight 

 of vapor in the air. The whole set in English measures, and Table Y. in 

 French measures, have been prepared for this edition. Being based on the 

 best elements we now possess, they are given here for ordinary use. The 

 second division contains the seven most important tables published in the 

 Greenwich Observations, and Glaisher's extensive Psychrometrical Table. 

 These tables being much used in England, and the results obtained by them 

 exhibiting no inconsiderable differences from those derived from the pre- 

 ceding ones, they are indispensable for comparing these results. The third 

 division, composed of ten miscellaneous tables, furnishes the means of com- 

 paring the different values of the force and the weight of vapor, especially 

 those which have frequently been used in Germany, and also of reducing 

 the indications of Saussure's Hair-Hygrometer to the ordinary scale of 

 moisture. The Appendix has remained as in the first edition, but all the 

 tables have been revised and corrected. 



The Barometrical series, now in four divisions, has been increased from 

 twelve to twenty-eight tables. Excepting three small tables for capillary 

 action, all the new ones 'have been computed for this edition. The com- 

 parison, now so much needed, of the Russian barometer with the other 

 scales, appears here for the first time. 



The Hypsometrical series is almost entirely new. It contained only Del- 

 cros's table for barometric and Regnault's table for thermometric measure- 

 ments, besides two auxiliary tables and the thirteen small tables of the 

 Appendix. It now offers twenty-three tables for barometrical measurement 

 of heights, in which all the principal formulae and scales are represented ; 

 three for the measurement of heights by the thermometer, in French and in 

 English measures; and a rich Appendix of forty-four tables, more extensive 

 and convenient than those in the old set, which afford the means of readily 

 converting into each other all the measures usually employed for indicating 

 altitudes. 



The series of Meteorological Corrections for periodic and non-periodic 

 variations, for all parts of the world, mostly due to the untiring industry of 

 Professor Dove, is an addition which will surely be appreciated by those 

 who know how difficult access to the original tables is for most Meteorol- 



