[ 204^ ] 

 XXX. Proceedings of Learned Societies* 



ROYAL SOCIETY. 

 [Continued from vol. xi. p. 196.] 



Nov. 16, *' "TAESCRIPTION of a new Barometer, recently fixed 

 1837. -^-^ up in the Apartments of the Royal Society ; with 



remarks on the mode hitherto pursued at various periods, and an 

 account of that which is now adopted, for correcting the observed 

 height of the mercury in the Society's Barometers." By Francis 

 Baily, Esq., Vice-President and Treasurer, R.S. 



The barometer, here alluded to, may in some measure be consi- 

 dered as two separate and independent barometers, inasmuch as it 

 is formed of two distinct tubes dipping into one and the same cistern 

 of mercury. One of these tubes is made of fiint glass, and the 

 other of crown glass, with a view to ascertain whether, at the end of 

 any given period, the one may have had any greater chemical effect 

 on the mercury than the other, and thus affected the results. A brass 

 rod, to which the scale is attached, passes through the framework, 

 between the two tubes, and is thus common to both : one end of 

 which is furnished with a fine agate point, which, by means of a rack 

 and pinion moving the whole rod, may be brought just to touch the 

 surface of the mercury in the cistern, the slightest contact with which 

 is immediately discernible ; and the other end of which bears the 

 usual scale of inches, tenths, &c. ; and there is a separate vernier 

 for each tube. A small thermometer, the bulb of which dips into 

 the mercury in the cistern, is inserted at the bottom : and an eye- 

 piece is also there fixed, so that the agate point can be viewed with 

 more distinctness and accuracy. The whole instrument is made to 

 turn round in azimuth, in order to verify the perpendicularity of the 

 tubes and the scale. 



It is evident that there are many advantages attending this mode 

 of construction, which are not to be found in the barometers as usu- 

 ally formed for general use in this country. The absolute heights 

 are more correctly and more satisfactorily determined ; and the per- 

 manency of true action is more effectually noticed and secured. For, 

 every part is under the inspection and control of the observer ; and 

 any derangement or imperfection in either of the tubes is imme- 

 diately detected on comparison with the other. And, considering 

 the care that has been taken in filling the tubes, and setting off the 

 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 t6 

 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 



