216 



These observations were made in January and February, with 

 one of Daniell's hygrometers, which was only graduated to 3°, 

 and thus for many successive days the temperature of the dew 

 point being below that point, the results above given are too high. 

 During the other months a capsule hygrometer, on the plan of 

 Pouillet, was employed. This agreed well with Daniell's on com- 

 parison, and seems to me a preferable instrument, as being less li- 

 able to be broken and requiring less ether. Having unfortunately 

 been broken in December, enough observations were not made in 

 that month to warrant the calculation of means. But on several 

 occasions deposition was obtained at — 10^, which was the lowest 

 point of the instrument. 



The barometer used is of the ordinary construction, with a 

 leathern bottomed cistern, in which, however the adjustment for 

 zero is made previously to each observation, by a delicate ivory 

 float, resting upon the surface of the mercury of the cistern, 

 which is thus open to the air; the 30 inches were measured from 

 the standard scale in the office of the Secretary of State. By an 

 intermediate comparison with that employed by Mr. Redfield, 

 of N. York, it requires a correction of -.04 of an inch. The tube 

 is well filled, and exhibits the electric light in the vacuum cham- 

 ber, is .16 inches in diameter, and the constant correction of .044 

 is added for capillarity. The attached thermometer is on the me- 

 tal scale, and the table given in Daniell's meteorological essays 

 has been followed in reducing the observations to the temperature 

 of 32°. The elevation of the cistern above low water mark of the 

 Hudson river, is 64 feet. The following table shows the monthly 

 means in the morning and evening, the mean of the observations, 

 the maxima and minima and range. 



January, . . . 

 February, . . 



May!'..*.*."/. 



July,'.*.*!! !! 



September, . 

 October, . . . 

 November,. 

 December, . 



, 30.160 

 . 30.169 

 . 30.082 

 . 30.102 

 , 30.006 

 . 30.079 

 . 30.101 

 . 30.062 

 30.006 

 30.178 



30.204 

 30.106 

 30.097 



30.021 

 30.048 

 29.992 

 29.995 

 30.159 



30.258 I 

 30.223 I 

 30.133 

 30.133 



30.054 

 .074 

 .077 



) 0.960 

 >0.810 

 ) 0.480 



Means, 30.1217 30.071 30. 1018 30. 828129.200 I 



The barometer is exposed on the exterior of the house, under 

 cover of a wooden shed. 



