VOL. XL.] PHILOSOPHICAL TRANSACTIONS. I67 



same day, and the barometers have been found to agree in their motions to an 

 liour, so far asunder as Townly in Lancashire, and Greenwich near London, 

 which is near l6o miles, though that might be partly accidental. The baro- 

 meter at Crane-Court and Southwick, distant about 55 miles, being compared, 

 seem very seldom to vary from their mean difference above -fV and 4- each way ; 

 at Southwick and Kent something more. From whence it might be expected, 

 that the weather should be much the same in all these places ; which yet seems 

 not to agree with accounts in some years from different parts in this island, not 

 very far distant : and Mr. Hadley has observed sometimes clouds to lie in one 

 part of the horizon for a great part of a day, which have discharged a large 

 quantity of rain in places not far off, while the place, where he has been, has 

 all the while enjoyed fair weather, and vice versa. Whence it appears, that the 

 barometrical alterations of the air extend farther than their effects, as to the 

 production of rain, at those times. Comparing the diaries of Crane-Court and 

 Upsal, he finds the barometers vary from their mean difference an inch and half 

 each way; Crane-Court and Padua as much, or more, and often go a pace quite 

 contrary ways at the same time, and their monthly differences are also very 

 variable, so that their agreement at any time seems to be but accidental. 



Secondly, he observes, that the descents of the mercury below the mean 

 heights of each place, taken in this way of Dr. Jurin's, are generally much 

 greater than the ascents of it above; and there are also other extraordinary de- 

 scents of the mercury in every year, of the same kind. The reason seems to 

 be, because the expansion of the air, by which it becomes lighter in some one 

 place, being the original of the alterations in the atmosphere, its effects by 

 condensation or accumulation of the air, in the places round about, will be more 

 dispersed, and therefore less sensible. 



Thirdly, the variation or range is greater the farther north, as has been 

 heretofore observed, and appears in these tables; and likewise it is greater ge- 

 nerally in the winter than summer months. The sum of the motion of the 

 mercury upwards and downwards, taken from the Berlin wandering line, with 

 a pair of compasses, in the year 1726, amounts to about 7^ inches, which gives 

 54^ for a month, and about 0.21 for each day. But the barometer is by much 

 most steady in the summer. 



4thly, The mean height of the barometer has already been applied to deter- 

 mine the respective heights of places, and also the absolute height above the 

 surface of the sea. Dr. Scheuchzer, in his Tables published in the Transac- 

 tions of this Society, N° 405, 4o6, supposes, from Mr. Marriot, the mean 

 height at the surface of the sea to be 28" l'" Paris measure, which reduced to 

 English, gives 29 inches, .993. This agrees very well with a Diary commu- 



