PREFACE. 



In May of 1847, I procured an open cistern barometer, made by Mr. AVilliam 

 H. Temple, of Boston, with a micrometer screw for the adjustment of the surface 

 of the mercury in the cup to an ivory point. It was similar to others Avhich he 

 had constructed for the use of the coast survey. The Vernier is moved by rack- 

 work, and reads to the one-hundredth of an inch. The interior diameter of the 

 tube is very nearly three-tenths of an inch. In the reduction of the barometric 

 observations, no account has been taken of capillarity. • 



The reductions to the temperature of 32° Fahr. and to the sea-level, with the 

 exception of the last year, were made under the direction of the Smithsonian 

 Institution, by Prof.. J. H. Coffin, of Easton, Pa. The reduction to sea-level was 

 based upon the result of direct experiment. The barometer, when standing at or 

 near 30.00 inches, with steady weather, was several times transferred from College 

 Hill to the water-level, and the mean result gave for the reduction +0.18 of an 

 inch. This is the correction which has been employed. 



Several different thermometers have been used, but always the most accurate 

 which could be obtained in this country. For the three years (since April of 1857) 

 I have used the thermometers made by Mr. James Green, of New York, and 

 known as the Smithsonian thermometers. 



The actual times of observation have sometimes differed a little from the hours 

 indicated at the head of the columns, although as a general practice the observations 

 have been made very nearly at the times specified. The direction and force of 

 the winds, and the degree of cloudiness have been determined without the aid 

 of special instruments. From the nature of the case these observations cannot 

 lay claim to any minute accuracy ; yet it was thought desirable, and not without 

 its utility, to make a record of the facts as they would appear in the judgment of a 

 practiced observer. 



Besides the deductions which appear on the current pages of the work, an 

 appendix has been added, containing elaborate summaries, which it is hoped will 

 facilitate the researches of scientific meteorologists, and thus repay in some degree 

 the labor which has been bestowed upon them. 



I may state, in conclusion, that all due care has been bestowed upon the prepa- 

 ration of the manuscript, and upon the correction of the proof, as the sheets have 

 passed through the press, with a view to prevent and exclude errors. But in so 

 large a mass of figures it is hardly possible to secure entire accuracy ; and I can 

 only hope that any errors which may have escaped notice will not be such as to 



mislead the inquirer. 



A. CASWELL. 



Providence, ./mir (i, 1R(!0. 



