Page:Proceedings of the Royal Society of London Vol 4.djvu/24

Rh 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 barometcrs, 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 prtserve 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.

MnBaily 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 Sooiety, to be involved in some confusion and uncertainty. Thus, prior to the year 1823, the cistcm of the barometer is said to be 81 feet above the level of low-water spring tides at Somerset House ; out 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 83 feet 2-;- inches above a ﬁxed mark on Waterloo Bridge ; or “ above the mean level of the sea (presumed about) 95 feet.” The discordance between the 81 feet and the 100 feet is easily accounted for by the fact that