2 



scale, it may justly be considered as a standard barometer. The pre- 

 sent volume of the Philosophical Transactions will contain the first 

 register of the observations that have been made with this instru- 

 ment. 



Mr. Baily then enters into a description of the several corrections 

 that are required for the various kinds of barometers, in order to 

 make them comparable with one another ; and treats of each of these 

 in their order. First as to the correction for temperature, both of 

 the mercury and of the scale : next for capillarity ; and afterwards 

 for the height of the barometer above the level of the sea. A table 

 is given for the first of these corrections ; and a convenient formula 

 for the latter : the correction for capillarity is constant, and of very 

 small magnitude. 



The author next describes the mode in which the observations of 

 the barometer have, from time to time, been recorded in the Meteor- 

 ological Journal of this Society ; and points out several inaccu- 

 racies which have occasionally been committed in this depart- 

 ment, for want of an uniform plan of reduction. Now this state of 

 confusion and uncertainty he remarks ought not to exist in a me- 

 teorological journal emanating from this Society, more especially as 

 the true values are as easily attainable as the approximate ones. 

 And although, in a general point of view, the minute differences 

 caused by such errors may be unimportant, yet as appeals are fre- 

 quently made to the barometer of this Society, as a standard, by 

 persons engaged in important researches, the most scrupulous accu- 

 racy ought to be adopted and pursued, and the fullest explanation 

 placed on record. And Mr. Baily says that notwithstanding the de- 

 tails which he has given may create some doubt respecting the ac- 

 curacy of the past, yet he is persuaded that the system now pursued 

 will inspire more confidence for the future. It is on this account 

 that he has entered thus at large on the subject ; trusting that what 

 he has stated will not only tend to preserve for the future a more 

 correct and uniform system, but also justify the Council in directing 

 that the register should henceforth contain the daily observations 

 uncorrected, and thus prevent the possibility of any similar confusion 

 and mistakes hereafter. 



Mr. Baily then adverts to the height of the Society's barometer 

 above the mean level of the sea ; a subject of much interest to many 

 persons engaged in various pursuits, but which appears, from the 

 notes attached, at different periods, to the meteorological journal of 

 this Society, to be involved in some confusion and uncertaint}^. Thus, 

 prior to the year 1823, the cistern of the barometer is said to be 81 

 feet above the level of low-water spring tides at Somerset House ; 

 but without any information how this was connected with the sea. 

 From 1823 to 1825, both inclusive, it is said to be 100 feet above 

 the same level. And from 1826 to 1836, both inclusive, the above 

 indication is omitted, and the height is said to be S3 feet 2^ inches 

 above a fixed mark on Waterloo Bridge ; or " above the mean level 

 of the sea (presumed about) 95 feet." The discordance betAveen 

 the 81 feet and the 100 feet is easily accounted for by the fact that 



